Run the Disk CleanUp utility.
You can find it in Start->All Programs->Accessories->System Tools.
And perhaps you should remove any and all unused software, like toolbars and crap like that.
While you're at it, install and run SpyBot Search And Destroy. It will detect and remove any and most malware/spyware/crap-ware/tracking-cookies that has been installed both with or without your knowledge.