I can't resist but to chime in on this
I see no reason for buying a new version of Windows. Win XP is solid and as Ritho stated Xp will continue to recieve support to 2014.
I would suggest a dual boot machine. You have plenty of hard drive space. You could carve out 20 or 25 gigs for a Linux distro. This will be plenty of room and you will still be able to download and install a ton of linux apps and games too

If your curious about linux this will be a great way to learn.
(and its Free)
For now I suggest sticking with Windows. Linux requires a bit of learning about the nuts and bolts. Meanwhile you will continue to have Windows available to get things done.
Cheers
Wdhpr