Yes, its free, It scans online, so you don't need to uninstall Norton.
If you caught the virus from Windows Live Messenger, it will have been from someone who uses P2P programs. In Windows Live Messenger go to Tools > Options > File Transfer and click Scan files for viruses using: Click Browse and navigate to your norton .exe then click Apply then OK. If you don't want to do that, click Install for the Windows Live OneCare safety scanner (also free).
This will scan every file you send & receive