Hey man, don't get down about the HID. You could definitely use them it's just going to require a concerted effort to keep it cool in that space. If you are dead set on using HPS, I would get 2 150w and run them in a straight line with some cooltube/air cooled hood to get rid of the heat. Take a look at the drawing i attached for clarification.

I think that'd work great. it just might be easier with T5s or CFLs. If you haven't checked out any CFL or T5 grows, i suggest you take a look. ICMag.com has a great micro grow section. Also check out their 150w HPS club. i think you'd be inspired by something in there.

sweet.
Skeet.