Compress my video

[Panoramixe]

Like anyone with a brain and an internet connection I've compiled a fair amount of video material, say a few hundred gig. The problem is I'm currently running out of disk space and not going to invest much until after my holidays (if anything is left then).
So when buying a 2 tb external hard disk is out of the question atm, I'll go for option b. So do you know of any good programs to perhaps even half the file size of the stuff I have?

Some info:
- It has to be (near) free, I'm in college so beer money > food, techno-stuff, ...
- It has to reduce the file size significantly, as a reference I have a few series of which the average file size is 350mb (for ~42 minutes) I believe I've seen decent quality video of that length for as low as 100mb. (.mkv perhaps?)
- The quality of the video doesn't have to be amazing, I use a laptop to watch the stuff so as long as the quality is decent I'll hardly notice a difference.

I'd greatly appreciate any input.

[Cilraaz]

The problem with video compression is that you lose quality that you can never gain back. Make sure you do a few test compresses before you settle on a format, a codec, and settings.

I would suggest using something like VirtualDub to re-encode the videos. I believe lately I've just been using the Xvid codec, though I'd have to double check at home to be certain.