I've got a bunch of messy midis that I got from a friend that have a lot of mistakes...I'd like to edit them since I'm familiar with the songs, but I'm not sure how. Is there some program to use?

It depends on what you want to edit it and how. I don't really know of free programs on the net which can edit MIDIs, but I do know of Anvil Studio which you can use to edit the MIDI.

Alternatively, you can use programs such as Cubase, Sony Acid or even notation softwares such as Finale and Sibelius. Do note that in Finale and Sibelius, you will have to edit the MIDI with another MIDI editing program to correct the dynamics and musicality (This is from experience). I would recommend Cubase 5 as it is easy to edit the MIDI with the piano roll editor.

Hope this helped.

Check out Reaper. It is a sequencer which you will be able to do a lot more with it: http://www.reaper.fm/ You will have full access to everything in the evaluation.