GRUB problem
 

I have reinstalled Windows XP and now I can't boot into Ubuntu because GRUB no longer appears. Does anyone know how to remedy this?

i know what the problem is, but i dont know how to fix it.

install windows xp first then linux == good
install linux first then windows != good

basically winxp probably 'repaired' your mbr.

well, there's a few things you can do...

before I start, I hope you have a bit of Linux knowledge.. either way, I'll try to explain as best I can...

Get a bootable linux CD that a) has a rescue mode b) is a live CD. Whatever the case, you need to get to a linux prompt.

From there, mount your hard drives. let's pretend your root (/) drive is temporarily mounted as /mnt/root and your boot (/boot) drive is temporarily mounted as /mnt/root/boot. That'd usually be done as:

mount /dev/hdb3 /mnt/root
mount /dev/hdb1 /mnt/root/boot

Where hdb[3,1] is your hardrive/partition that linux exists on. I'm not sure how Ubuntu creates the partitions (or what partitions it creates), so it's hard to elaborate on that. I am guessing that Windows is on hda1 (first hard drive, first partition) because it usually doesn't play nice with anything but that (although there are ways to trick it).

Anyways, once you have them mounted, chroot to /mnt/root (type chroot /mnt/root), now it's like you're on your system normally.

From there, you should be able to type "grub-install /dev/hda" to put grub back in your mbr (master boot record).

I hope that helped somehow.. it's fairly technical, I know... but it's the best suggestion I have at the moment. You may be able to google for better instructions (I haven't checked).

I ended up reinstalling because the Live CD I have wasn't able to load properly. I think there was a problem with X server or something similar. This must be the 7th reinstall in 7 days...:(

I wouldn't call them "reinstalls", I'd call them "learning experiences" :)

Seriously.. reinstalling sucks, but at least you keep learning things as you go along.