Do you have virus protection for your computer? I use Norton Internet Security 2009 (also previous versions) to protect my PCs. NIS includes anti-virus, anti-malware, and anti-spyware functions. It works fine for me, although I have to update it (virus definition etc) constantly. It will cost you about $60 per year to protect up to 3 PCs.
At some point, my Windows XP PCs all forced me to install "Windows Genuine Advantage" to validate my OSs. I think it is probably the same case with Vista.
If Vista is a pain to you, you may want to try Ubuntu 8.10 (32 bit or 64 bit version):http://www.ubuntu.com/getubuntu/download
It is free and will always be free. I tried it and it worked fine for simple tasks such as web browsing, e-mailing, and office work (Open Office, includes Word Processor, Spreadsheet, and Presentation). Another advantage is that you don't need to worry too much about virus, esp. the 64 bit version.