I dual boot Windows 7 with Linux Mint. Now although Linux doesn't need Antivirus, choosing the right one for windows can often be a tricky task. I've tried dozens and the best three in my opinion are:
Microsoft Security Essentials Avast! Home Edition AVG Free
Feel free to use any of the suggested programs as they are all free! If you want my PERSONAL opinion on what I think you should do however, then I think you should go with Microsoft Security Essentials. It does what you need, by itself. Auto updates, auto scanning, AND, it's non intrusive!
Regarding Microsoft Esseantials......does it include a Firewall to replace the one supplied with XP, as the one with XP only gives one-way protection? Windows Live OneCare included a replacement Firewall. Can't see any mention of this on the links.
Thanks Sea Urchin.....will probably use Microsoft Essentials! I have another month to go before WLOC expires but would like to find a Firewall to replace the XP default version in the meantime. Is Comodo free?