[jtroutma]

I would probably have to agree with TerraMex.

I ran into a similar situation where I built a system for a friend which consisted of a ABIT NF7 in a mid-size case with a 80mm intake over the HSF + 80mm intake (front of case) and only the PSU to remove the heat. The CPU was an Athlon XP 1700+ Running @ 2100Mhz at about 47C with cover off. Once the cover when on, the temps jumped to about 52-55C. I then added an additional 80mm exhaust fan and the temps went back to 47C.

With the setup that it SOUNDS like you have, see if you can take one of those 80mm fans and make it an exhaust fan near the back of the unit and then add some air holes near the front.
Reason: More air going out of system than into system creates a slight vacuum effect inside the case causing air to be pulled from the outside of the case inside. With the air being brough in from the front and forced out the back, you create a wind tunnel inside the case => very good airflow throughout entire case. (Worked wonderful in an external SCSI case that I made for work!)

Good luck.