Ya know, I have a desktop with windows vista and a laptop with XP I am running AVG in both. I love it it has actually thrown up pop ups stating it has blocked unwanted sites. I recently deleted AVG. thinking naaa who needs this after surfing the web for some time, I got a worm ( in the vista ) i was devastated.  I got rid of the worm with a system restore. then redownloaded  the AVG program. no more worries.PC World recommends AVG. I did the research. check it out,  pcworld.com