Unsuccessful partitioning...

Windows is particularly bad at figuring out how to partition a drive. If you left your OS X partition active, windows sees it as if it were the only partition in existence.

Windows wants to be on a primary partition. It wants that partition to start before a certain cylinder. When I have set up multi-boot systems, I have made the windows partition at the beginning of the drive then marked it active so windows could find it. Of course, once the windows partition is marked active, the only way to get back to my favorite other os is to go mark that partition active. In the "bad old days" I used to do all this with partition magic under windows. I'm sure there is an equivalent way to do this under OS X. There is a limit to how many partitions can be primary. I think it's 2 or perhaps 3. When I googled for boot camp windows partition, I found an article suggesting you put the windows partition at the end of the drive. This might work for Vista but not for XP. Try to find a way to move the windows partition closer to the beginning of the drive and XP should install just fine. At every point during the install, make sure it reports the available space as the partition you set aside for windows and no more or you might find yourself with a wiped machine booting from your OS X dvd to try and bring OS X back.