Step1: Anti-virus
Get and install avg (http://free.avg.com) or other preferred antivirus software.  The free version of avg should be fine.  Avg is pretty straight forward.  Install it and run a system scan.  Now go read a news paper, take a nap (or goto bed depending on how much stuff you have in your computer), read a book…  do something that is not watching your pc scan.  Come back.  Did the scan finish.  Did it find the virus?

If avg found (and was able to clean/delete/quarantine your virus, you should be done.  If your virus is capable of defending itself, you may have to move on to step 2.  Now, if avg closes when you try to install or run it, then your virus is monitoring your actions and attempting to defend itself.  If this happens move on to step 2.  If the virus is gone, then leave avg installed, as it will continue to protect your system in the future.

Step 2: Spybot S&D (Search and Destroy)
Ok, so for whatever reason step 1 didn’t work.  It’s possible that avg didn’t have a definition for a piece of spyware, as spyware isn’t technically a virus (but avg does defend against most anyways.  It’s possible that the virus defended itself against avg, or even prevented you from opening it.  Lets try step 2.  Get and install Spybot Search and destroy (http://www.safer-networking.org/en/download/index.html).  During the install, spybot will want to do a few basic things.  Don’t bother backing up your registry, as it is already probably infected.  Get the updated definitions (or copy them over if you have them.  Yes you want to install the tea timer.  Run a scan.  Do more of whatever you did while the antivirus was scanning in step 1.

Did Spybot find you’re problems: Good.  Note, that spybot will usually find a few things wrong with your system, but it might not cover your virus.  Remember, there are defenses that viruses can use to defend themselves and hide from the software, if they were there before you installed the software.  If spybot S&D does get rid of your virus, then you are done.  It is recommended that you leave spybot on your computer so that it can continue to provide protection.