removing ubuntu and installing xp should be easy. Not that you'd want to. ubuntu is far superior to any windows release in almost every way.
I play video fine, the quality is good. Only thing is the annoying lockups I get. but these aren;t because of playing the files, that's a far deeper routed issue.
and as for battery life... I get a shade off 2 hours with a 3 cell. I have brightness on my monitor almost all the way up though, and it's in constant use for those two hours. If i left it with the screen locked for that amount of time, I'm guessing it'd be way more.