I had this virus last week. I was infected with W32.IRCBot (norton detected it). If you do a search in Google for W32.IRCBot removal, there are some useful links to Symantec, providing information about removal. If you have any Anti-Virus software, do a full system scan and the file should be picked up. In the mean time, delete the file you originally downloaded (C:\Documents and Settings\[your user name]\My Received Files). It should be a ZIP folder called "Image [random number]". This won't get rid of the virus, but it should stop it from coming back after removal.
I wouldn't use MSN untill the virus is fully removed, otherwise all of your contacts are likely to receive the virus.
If you don't have any Anti-Virus software, get some, I would go with Avast! (www.avast.com
). Its free for home users, and is (I'm told) very good.