For me it’s a fact by now. Every time i decide to install WinXP back onto my laptop, something goes wrong. Big time.
After creating a 25 GB partition on my laptop i proceeded into installing Windows Xp Sp2 (which the laptop had preinstalled anyways when i got it).
The installation went smooth enough and as expected the MBR is messed up at this point and the computer boots directly into Windows.
As done a few times before, but still worth mentioning, the procedure in these cases is:
1. Boot the Live CD
2. Open a terminal window and type:
sudo grub
3. On the new prompt:
grub>> find /boot/grub/stage1
the answer in my case (hd0, 0)
4. Proceed
root (hd0,0)
setup (hd0)