Trying to install Ubuntu alongside Windows XP

[alexseanchai]

I've got an 80GB hard drive on this machine. One partition's Windows, one is Linux swap space left from before I reinstalled Windows, one is mostly just there, and I want to install Ubuntu on the fourth. Trouble is, every time I try, my choices are install on the whole disk and install on the whole disk. Except for the time I tried with a flash drive in; I now have a 16GB flash drive with a 10GB partition Windows recognizes and a 6GB partition from which I can boot Ubuntu.

I don't want to install on the whole 80GB disk. There's a reason I reinstalled Windows. I also don't want to boot from a USB anything, because every time I try to boot Ubuntu I have to glare at the 'This is not a bootable disk' message until I remember I need to disconnect the external hard drive before the computer thinks to check the flash drive.

What do I do?