Start with Mad Cat - You know that mad cat they took down in the cut scene? Well, the story is that you get it. Go here to download the files needed. I'm not sure if this is an official patch or not but it was on the official site.

The Demo - There is a demo for MechCommander, however its around 111.1 MB!! The only place that I can find it at the moment it File Planet - but i'm not going to make you register to get the file! :P. When I have time I will look for it - and find it... Somewhere...

MechCommander Gold Patch - FASA have released one patch that is used in mutliplayer stopping a jump cheat. Again like the Demo I can only find this on File Planet at the moment.