Hmmm...
First off- Welcome Aboard!

Hopefully you'll stay a while and learn a lot- which is what I did. There's tons of stuff to learn here and a lot of helpful, friendly folks.
So- that's a decent sized question. I'm a pro tools guy, though, so I'll do my best.
Forgive me if you already know some of this stuff.
Get to know the RTAS (real time audiosuite) plugs and how to use them. In the mix window you can usually see the inserts and sends areas at the top of the channel strip. If you insert an RTAS plugin up in the top section, you can adjust the settings and try out different presets in real time. Your 'Getting Started with the Mbox" manual should have clear and simple instructions for how to do that.
So-on to the plugs. For compression, and maybe even hard limiting, check out the BF76.. Its in the RTAS menu of the mixer (when you go to add and insert) in the Dynamics folder. The ratio buttons are right next to VU meter (4,8,12, & 20 I think). Try 4 or 8 for compression and 20 for limiting. Attack and release controls are the smaller knobs. The input knob is how you set your threshold (watch the meter to see when your signal starts hitting the limiter) and the output know is your make up gain.
I don't like the other compressor and limiter plugs that come with Pro Tools, but check them out anyway.
Sorry- all I have time for at the moment. I hope that at least a little helpful.
Chris