I think Windows 7 comes with McAfee anti-virus software. Norton 360 was installed also. Can I leave both of them on, or must I get rid of one of them? Does having two cause problems with programs I'm trying to use?
You should try posting your question in a different forum. This forum is for something very different from what you're asking.
However, to answer your question, it's generally advised to only have one virus scanner installed. You might want to consider uninstalling both Norton and McAfee and instead installing this free product from Microsoft:
http://www.microsoft.com/security_essentials/