Thank you to all vista haters for giving no help at all, no one cares if you don't like vista, some people actually enjoy its features.
As for your problem, the above mentioned virus theory is most likely right. The thing is that when you go to delete it, the file is in use by a service, so you cant just delete the file. Solution?
Start your computer in safe mode (hit f8 before windows loading screen appears). This will NOT load all the usual processes and services during startup, i.e. the .dll file. This way you can delete the needed file, then restart windows.
Hope this helps!
Go Vista!