What would I need to disable clients from linking things on my servers from a page on another server? I know some webhosts do this and I'm looking for a program like it. What would even be better is if there is an option to only allow this for files larger than X MB's. That way pictures could be linked off site, but not other files.

This may help you:

http://webhostingtalk.com/showthread.php?threadid=3065

If you need to link off-site, you can adjust your mod_rewrite code to cope with that location as the referer. It will deny the images to domains that aren't on the list that you've specified.