I have 8.04 installed on a USB hard drive that I dual boot on my system.

I select the boot drive at boot time through the bios, as my wife is a
Windoze user only and doesn't want any hassle at boot time.

When I installed 8.04, I did a manual install from the menu.

I had it put the install and GRUB on the second drive. (It saw it as
just another drive.)

I had to edit GRUB to get 8.04 to boot properly.

When you install it like that, GRUB sees the second drive as Drive 1.
But when you boot from the second drive, GRUB sees it as Drive 0. So
I had to change the entry to boot from 0,0 rather than 1,0.

This way Linux gets too boot from its own loader and Windows gets to
boot from its own also.