It's just a basic airflow problem. Try it with the case cover off before you add more fans.
Another recurring issue are power supplies that are taxed to the limit. You'll want the 450Watt or larger PSU. Tax that PSU and it generates more heat as well.
First off, let me say that I know very little about hardware...I'm more of a software guy. That being said, a few days ago, I built this new PC:
Chaintech V915P Mobo
GeForce 6200 256mb video card
1gb 3200 Corsair Ram
120gb Western Digital HD w/ 8mb cache
Intel 3.0ghz Processor 1mb cache (Socket 775)
The processor is the problem I am concerned about. it's running at 60C at idle. i have 2 80mm case fans in it. But I'm going to be adding more. I would like to know how I would go about cooling it down. Just looking for suggestions. I'm thinking I might try a third party heat sink, right now I'm using Intel's.