I assume you know about Wubi as an alternative way to run Ubuntu.

Two, or more hard drives will work just fine with Ubuntu as long as the
Linux is installed after the Windows. You shouldn't have to change the boot
drive in the BIOS as the Grub startup menu should find and include all
operating systems on all drives, as long as it is on the boot drive. That
is what I have: Win7, which came with my HP system on the first drive,,
sda, a drive for storage and sharing formatted with fat32, sdb, and Kubuntu
on a third Hard Drive, sdc. Any operating system can be chosen from the
grub start menu.

Yes, that works. If your computer has a built in boot manager (most newer
computers do) then you can press a key (mine is ESC) that will show
the available HDs and it will allow you to select one from the list. That
way you can have two bootable sectors and you just need to point to them.
You can even have different versions of GRUB on each drive or GRUB on only
one and Windows with its own boot manager on the other. You just have
to know what you are doing when you set it up.

I have used WUBI, dual boot, VMs, Qemu, KVM, etc. But now prefer two
separate computers. One for Windows and one for Linux.

How about hard drive pull-out drawers, since colleges use these for various
reasons? I don't know how you'd keep the 2 active hard drives from seeing each
other after boot-up, perhaps a clash might happen. A slave drive could be used
for shared data files and Home, so you could try various Linux installs, too.

If using Visual Basic on a course then I'd recommend a native install
of Windows, i.e. full dual boot, as you'll be writing code that may
need direct access to the hardware and the last thing you want is to
have your code not working and it not being the code itself but not
being compatible with a virtual OS ( i.e. running Windows 7 inside
Virtual Box )

If you've already got Ubuntu installed then adding Windows 7 as a dual
boot is messy so your idea of separate HD's is a good one, whether
it's by selecting them on boot or removable drives. What would be a
good idea is to disconnect the Ubuntu drive when installing Windows as
this could cause installation hiccups.

Would an external HD work for installing Win7? My internal HD is a SATA II.
WOuld the external drive need to be a SATA as well?

Linux can boot off USB externally, I haven't tried Win7.

Yes, you should be able to install Win7 on an external drive. It could be
either PATA or SATA; both will work on the same machine. It should be
connected internally to the appropriate interface. As far as the Operating
System is concerned it's just another drive. I'm not sure it would work if
it was a USB drive - it might.

If the external drive is USB then it won't matter if the drive inside
is PATA or SATA however it will run slower than if used on an internal
drive. Best would be to fit an eSATA card and use an external caddy
that has eSATA connection - that way you get the full interface speed.

Regarding USB - if you have a USB3 port then using a USB3 caddy will
also give you full speed but at a higher cost than eSATA until prices
of USB3 devices start to drop.

Just a warning if using an external caddy - be sure not to disconnect
accidentally when booted into Windows. At the least it will corrupt
data and at the worst totally trash the OS

I found an internal 500gb HD that should work fine. So the process is to
disconnect the HD with Ubuntu on it and then install Win7 on the new HD?
Will Grub get loaded after I re-connect the Ubuntu HD?

Grub is never automatically reloaded but can be reinstalled. It's fairly
complicated and I've only done it once.

Whether your system will now boot to Linux depends on where you told the
Ubuntu installer to put the grub startup menu, probably on what was the sda
drive but now will be sdb. If Windows is on the first drive Ubuntu won't
boot unless you unplug the windows drive, and make the Ubuntu drive sda
again. That is worse than an inconvenience...

There is a fairly easy to use repair disk that will fix this so you will be
able to choose the operating system from grub as you boot up the computer.
It is available at https://help.ubuntu.com/community/Boot-Repair . It's
saved my bacon more than once!

I don't have the new HD for Win7 yet. When I get it, do I make it the Slave
and the Ubuntu HD the Master? Sorry, this is all new to me.

It doesn't matter as long as you know which you are going to boot from. You
will need to run the boot repair disk if you install Windows after Ubuntu
as Windows will wipe out the Linux Grub boot menu.

No such thing as Master and Slave now with SATA drives and is also
meaningless on external drives connected through USB anyway.

When you reconnect the Ubuntu drive two things will happen, 1) Windows
will ignore it 2) Ubuntu will add Windows to the boot menu if you boot
with the external drive attached and run sudo update-grub.

What you will need to do is use the 'Select Boot Device' key on boot
up to choose whether you want the internal drive with Ubuntu or the
USB drive with Windows. Often this is [F12] but my system uses [F11]
and I've seen [F8] used for this too ( really silly as it interferes
with the boot into Safe Mode in Windows ! ).

If the motherboard doesn't have this option ( and it even may need to
be turned on in BIOS ) then you'll have to manually select the boot
drive in BIOS each time - hope not as this would be a pain

You can install Windows 7 on the separate drive and do not need to
disconnect the Ubuntu one. You might want to switch cables so that
Windows will appear first and be the traditional C: drive. Otherwise
it will want to format your C drive at regular intervals (which will
have Ubuntu on it). If Ubuntu is on D: then it seems to ignore it.
Some applications will only install to C: in Windows.

You will need the Ubuntu live disk to fix grub because it will have
Ubuntu configured to boot from sda when it is now sdb. It is an easy
thing to do. You will likely have to do this in any case. The rule of
thumb is install Windows first and Linux second. The only advantage of
disconnecting the Ubuntu drive as far as I can see is to simplify the
process, as you will not get confused with drive letters.

You can write grub to either disk or both. My preferred method with
two drives is to leave Windows with the Windows bootloader and write
grub to the second drive. You can only boot into Linux with this
method by pressing a key to get to the second drive by a boot manager.
It can be a nuisance if you regularly shut off the computer, so in
that case I would just write GRUB to sda or C: which is the
traditional location. I use a desktop computer which runs 24/7 and
seldom re-boots. I like it that way for security. A nosy person who
chose to power off from the locked screen would discover that it would
boot into Windows which has nothing on it. They could not get into
Windows either since it is password protected.

I regularly rewrite grub. I install dozens of distros and each one
rewrites GRUB to make itself first and not all are equal. Some distros
do not recognize all distributions and make a grub entry for it.
Ubuntu has one of the best for that. I say this only to point out that
rewriting grub is a simple matter and not to freak out if you cannot
get into Ubuntu after installing something else.