I havent dont fully professional commercials, but your best bet would be a nice DV camera that records on mini DV disks, and a firewire card for your pc. Premiere is the best for editing. For audio I have used CoolEdit 2000 with good results.
If you feel that your budget does not allow for this equipment I reccomend a Hi8 camcoder, capture in DivX format in virtualdub with any capture card that has S-Video in, edit with premiere and output to tape with TV Out.