Unless someone has specifically changed the file type association (why?), a .vbs file would normally be set to open with Wscript.exe (1st) or alternatively Cscript.exe which are both part of Windows.
As somebody asked before what's the name of the .vbs it wants to open ?
If you don't have AV software installed already you might consider having Trend scan your system via the web. See:
http://housecall.antivirus.com/housecall/start_corp.asp