Most of the units I've worked with have the power supply fan blowing air OUT the back. The theory is cooler air is sucked in from outside the case where it cools the system first, as opposed to pre-heating the air with the power supply :-)
You can easily check this by holding a small bit of tissue paper or cotton up to the fan. It'll either get blown out, or try to get sucked in.
I agree with Ilwrath, one of the best case cooling solutions is a 2nd fan forcing air in the front.
You can set up ducts and dividers to get airflow where you want it as well.
Try to get a fan with a dust filter attached. The main problem with fans is the amount of dust and crap they suck in.
Do you think it's heat causing IB to crash?
If you get lots of weird system behaviour and crashes after running it for a short time, this might be the case.
Also try gently flexing the motherboard by pressing down on it while it's running. If pressure in a certain location always results in a freeze or crash, there are possibly solder joint problems, or connector problems (memory SIMMS, CPU board connector).
In the case of a bad solder joint, it's a matter of reflowing all the components in the suspect area, often fixes it. You'll need SMD tools and good soldering experience to fix it properly.
Clean all connectors (Zorro edge connectors, memory, CPU board) using a small brush and isopropyl alcohol, or better yet, use one of the special lubricating/cleaning sprays for gold plated contacts.
