What is a program compresses larger files into a smaller file?

There are a variety of programs available to compress large files. Winzip, Winrar, Zipgenius, Stuffit, Winace, etc. I prefer zipgenius. It's completely free and offers all of the nice features that the other's provide.

http://www.zipgenius.com

Now, consider that this won't reduce very much on files like mp3, avi, or jpg because they are already compressed versions of an original. If you are looking to reduce the file size for emailing purposes, you'll have better luck using a third party large file transfer website. I'd recommend toobigforemail, they'll let you send up to 2gb with a free account.

http://www.toobigforemail.com