Also you should get the latest divx codec for a compression codec. Spend some time reading up on it and with a little tweaking it makes the best compression codec. Just hit the options button under the type button(in rendering options under the output tab). Then choose divx from the drop down list and hit configure. You need to spend a little time reading the divx how to guides on there website. It throughly explains the features in divx and gives good tips on encodeing.
http://www.divx.com/support/guides/
Divx gives Awsome quality with excellent compression. One tip on compressing, when you want to play with the settings and see how they affect the look of your animation just render a one frame animation with divx. Then view the one frame animation look it over good then adjust the divx settings and render again and you will see the difference in your setting changes. Also check the size of your one frame animation and you can esitimate how large the total rendered animation would be. The is a very fast way to tweak the divx settings and get a good looking frame with good compression without haveing to render the whole animation.