Right click on it and select properties. If it was in Windows\system32 then it should be the legitimate Windows file of that name, but considering where it is and that your AV says it's infected, I'd tend to believe it and try quarantining it.
Here's an example of a worm that creates a file of the same name but that is infected...
http://www.symantec.com/avcenter/ven...torvel@mm.html
Just because a file has the same name as a legitimate file, doesn't mean that it's not infected with a virus.