If you mouse over a link that might be dangerous and you don't click it do you still get the virus?

[Filenotfound]

Well it IS possible. But not on facebook, as you cant make your own javascript for the links so, you are fine.
But you could easily have it load a js script with the onmouseover(); command. So on other sites, its definitely possible, but not as likely.
As most other sites that will try to give you malware, will just have it do it automatically when you load the page.

If you are that worried about getting drive-by malware download you can do a few things.
1) run your browser from inside a sandbox or virtual environment. its the most efficient way to pretty much guarantee you no driveby malware downloads.
2) use browser addons. Use addons like no script or ad blocker plus and ghostery to stop scripts from running. Also would suggest something like WOT which help notify you of bad sites like that in the first place.