4 gigs for some of my installs. do this: dual boot first.
install firefox to the xp operating system first. import your book marks from ie(if you use it) to firefox. then when you install ubuntu will find them and carry them over.
defrag the hell out of the xp. see if you can get a defragger that does its work outside xp. it will be more effective. you want a nice open area at the back of the disk.
run the livecd. install. it will walk your through and i nabout 1/2 hour to an hour you should be ready. reboot when it says to, removing the cd.
Now you have an installed distro. You might have to configure the wireless again, but now you know how. Wireless cards can be iffy with ubuntu.
run your updates if asked for it, and finally, if it recognises a restricted driver, do that last. You MIGHT need to do an update after that, certainly a reboot, but 'buntu is really nice about not asking for endless reboots.
and that should be it.