Ridding your PC is perhaps best via something like Trend Micro 'HouseCall' so you just go to the site and follow instructions - needs you to approve a download or two and to run their software to scan your machine...
Also, you might be able to find some 'trial' version of Symantec (aka Norton) anti virus, or one from McAfee (for example, my bank, HSBC, is offering free use for a year on up to 3 PCs).
Before searching, I'd recommend going to a magazine website (eg ZDNet.com or webuser.co.uk) and look for reviews of AV software, so you can get the right website names for companies (else a search on Google etc may find some dodgy site, where they claim to offer an anti-virus but you are just putting something worse on).
It's common for Windows machines to be infected as the majority of users have the standard Microsoft items of software and things like address books are easy targets.
Might be worth using something like Mozilla Thunderbird for e-mail (once your PC is clean), and building up your address book on that, or using a free online e-mail service instead, for a few months.