Need some opinions!

Though I count Jeff Lenosky (Who designed the STP) as a friend, I'd prefer the Cromo frame. Unless the STP comes with a much better fork.

Is that a marizocchi on the STP? I can't comment on the Kromo as I never owned or ridden one... but I did enjoy the STP while I had it. However, both bikes will be great starter bikes before you figure out what feels good to you. For me I went from a P.1 to STP to Blk Mrkt MOB.

I went ahead and bought the Kromo. After several calls, texts, and e-mails to the guy with the STP and absolutely no response I decided to not waste my time on it and got the other one. I only paid $400 for it and it seems to be in almost perfect shape, no scratched whatsoever. But haven't been able to ride due to the snow we've got up here so I'm hoping next week I can go to the Boulder indoor cycling center just to break the bike in.

Good choice. Chromoly is sooo much nicer on a DJ frame, alu rides really harsh. You'll enjoy it. Parts are less important, at least in the beginning. Even the fork doesn't matter too much until you start going big - and then you can always upgrade.

Can a dirt jump bike do mountain biking? any ideas on how rough you can be with them ? my chain keeps on hitting the frame whenever i go over a small or medium bump in the ground so how much can it take?

yes, but you technically could ride a bmx on mountain bike trails, but it might not be much fun. You're not going to hurt the bike trail riding it, but the geometry is definately not made for trails. To prevent damage to the chainstays, you might consider something like this
http://www.chainreactioncycles.com/Models.aspx?ModelID=4760