If you are not using Windows Live OneCare, you are off topic for this forum. This is not a general forum for viruses, spyware, or Windows Help. For help with spyware issues, you may want to try the forums here:
http://aumha.net/ For help with virus removal, contact the maker of your Antivirus program.
However, I suspect that what you are seeing is that a spammer is using your email address in the from field for spam. That does not mean that they have hacked your account or have infected your PC.
-steve