First of all, on the Windows side, you need to share this printer. If
you are already using it on another Windows machine on the network,
chances are good you already are. If not, you need to select that
printer in the Windows Printers dialog, select "Sharing", check the
block that says you want to share this printer and give it a share
name (something simple would be good, as long as it identifies the
printer).

Next, you have to make Ubuntu "look" for network printers. If you
haven't done this before, go to the "System" menu, "Administration"
submenu and select "Printers". This will bring up the Printers
dialog. On the menu for this dialog, select "Global Settings", then
select "Detect LAN Printers". It will give you a warning about this,
that or the other, but you need to do this in order to see the printer
on your Windows machine. After you've checked this option, log off,
then back on.

Now go back to your Ubuntu computer and open the Printers dialog again
(under the System->Administration menu) and see if you can "see" this
printer. If not, you will have to double-click on the "New Printer"
icon and step through the process to add a network printer. I'm
hoping you won't have to.

If you continue to have problems, pm me, and I'll try to assist.