Hi Alexandre, and welcome to PSW. A few things to consider:
1) If it's not broken, don't fix it. Windows XP is certainly dated but not yet 100% obsolete. The IT experts here can certainly explain why surfing the web with Windows XP might be ill-advised, but otherwise if all the computer does is run CompuLive and still does so reliably I wouldn't mess with it. I still occasionally shoot pyro with a Panasonic ToughBook running Windows XP - just proof that old doesn't necessarily mean bad so long as reliability isn't compromised.
2) If you're going to spend money on an upgrade, make it count. There are lots of modern lighting control programs that could significantly benefit you, especially if you do or plan to control more than just 4 moving heads. A lot of these have programming and playback wings available for tactile control which really helps.
3) ETC is more or less the gold standard when it comes to theatrical lighting control. Their software offering is called Nomad and their basic USB-DMX interface right now is the Gadget II. I own this setup myself for instances where pulling out my full-sized console isn't necessary. ETC also offers a student bundle of this (last time I checked) for only $250 - very hard to beat for the name, support, pedigree, and capabilities that you'll get for that money.
4) Speaking of money, how much budget do you have to spend? Professional lighting solutions get expensive fast.
Hope this helps!