I don't know what I'm doing as far as computers and gaming stuff. I have a few games on GOG already, but I just downloaded Myst: Riven. It looks like it downloaded just fine, but my McAfee bitched about it and when I press PLAY it just clicks and nothing happens. Any ideas?

Try disabling the anti-virus and then playing it.

I'm not quite sure how to do that, or if I should. According to McAfee, part of the Riven file is infected with a virus. I tried un-'quarantining' it, and I disabled the firewall temporarily. Still nothing

Remove Myst.
Remove McAfee
Install better AV … Suggestions
Download Myst again.

It's what's known as a false positive -- that is, your antivirus deciding "better safe than sorry." It is usually due to the AV trying to match snippets of a file's structure with the structures of know viruses ("heuristic analysis"). If you poke around in McAfee's settings, you should be able to find a way to mark certain programs as safe (probably including after the AV program has already flagged it as a possible threat and quarantined it), as well as set exceptions for folders where you don't want McAfee to scan, such as wherever you have Galaxy installing your games.

There was another thread recently about a Myst game being falsely detected as a virus.

Unfortunately McAfee and Norton (Symantec) are some of those popular AV which are actually pretty bad. I would include TrendMicro here too.

McAfee is 100% known to be virus, stay the hell away from it, your much safer without any AV even the windows version is good enough as i've heard