Mixdown/Mastering Question..

Alright. I've got a "completed" track and I want to know a few things about the mixdown & subsequent mastering process. What is the goal during the mixdown? Checking levels, accuracy,etc? What does that entail in its entirety? Then, once I have a proper mixdown, should I leave it alone and let the engineers master it (assuming this track gets picked up) or should I go ahead and run the track through something like t-racks beforehand? Also, When mastering a track through software such as t-racks, is that track then "mastered for cd"? I know that mastering for vinyl, ala Neil/Simon/etc. is a whole different game, but is that what t-racks and other similar software applications are meant to produce? tracks mastered for CD? Someone point me to some links/help. I'm konfuzed something fierce. 8O