I have a 160g disk with 100g xp and 60g ubuntu partitions. I used [link|http://www.terabyteunlimited.com/bootitng.html|boot-it ng] to partition the disk prior to installing ubuntu - though i think it has its own partition resizer now.

I set it up 1.5 years ago, so ahve gone through 2 major updates of ubuntu and many xp shenanigans without issue. The only gripe i've had is manually cleaning up grub after kernel upgrades and the fact that it assumes ubuntu should be the default OS to start. All tweakable, of course - i just think it should ask ;) No operational issues with either OS whatsoever.

hth.