It's hard to say whether it's your wireless adaptor (= 'stick') or your computer that's at fault. Ideally I'd like to be able to test the wireless adapter with a different computer (and also to try other USB devices with your computer). If it's not possible to do that it might be simplest to buy another wireless adapter and give it a try. This does the same thing as your 'stick' and is unlikely to push you into bankruptcy!
http://www.kikatek.com/P266742/WL-700N-RXS-Dynamode-WL-700N-RXS-802-11n-Nano
At the same time, you might also want to consider whether you should be thinking of moving on from Windows XP. A Windows 7 computer costs very little these days:
http://www.accomputerwarehouse.com/products/computing/refurbished-computers
(That's not just a random web link from a bit of googling. It's where I got the excellent Windows 7 Pro computer that I'm now using. I've used that company several times and always had excellent products and service from them).