Assuming you've exhausted the partitioning options on the XP disk, does the BIOS contain a low-level format option? Needless to say you will lose all data ever but it might do the trick (if take a very long time). I don't have the laptop back until tomorrow evening, so I can't check right now, but ...

I was resizing the partition of a friend's laptop, and it ran out of battery mid-way. (I know, stupid me.) I've tried using an XP disc (with the SATA drivers) and it can't see the hard drive or any partitions. Ubuntu throws up a bunch of errors when using the Live CD and when trying to install, and ...