You can always set up a dual boot and try both out, or use one OS (Ubuntu) for al daily tasks and Windows for games that don't run under Ubuntu.
One pro for 64bit linux versus 64bit windows, most tasks/programs are 64bit whilst most programs in 64bit windows are 32bit running "emulated" tho you may never ever notice that.
As for XP vs Vista.
Wel forget XP 64 bit. The least supported OS next after ME.If you want to be sure "everything" runs get XP. That does mean however that you can't use more then 3.2 - 3.8 GB ram depending on the hardware and it is less secure.
If you want to run a 64bit Windows go for Vista. I've been running it since its release, almost everything runs on it except a few very old games. Most mainstream hardware has support for it. (And no, UAC isn't bothering me at all, I don't have the habit of installing new programs every second..)
And offcourse thins work differently in a Linux OS. The same way things work differently compared to AmigaOS or AtariTOS.. What's the point of having more OSes out there if they are all the same..
