Another note along those lines is that one fan blowing into or out of the case moves x amount of air. 2 fans blowing in or 2 blowing out moves nearly 2x as much air (small losses based on what the air flows over to get into the case and such. However, one fan blowing in, and one blowing out, only moves something like 1.5x as much air.

I took this to heart, and I've now got what I think is a proper solution.

For starters, I bought a replacement CPU cooler, a Zalman CNPS7000A-AlCu. This is a very nice unit. Fit perfectly in the case, and is orders of magnitude more quiet than the Intel fan and heatsink that came with the chip. Not silent by any stretch of the imagination, but a lot quieter.

Then I got two Vantech SF8025L case fans. Therse are medium-airflow 80mm fans. I didn't have an easy way of mounting a 120mm fan otherwise I would have gone that route. Again, these are not silent but they are reasonably quiet.

Mounting of the case fans was an adventure. There is one spot for an 80mm case fan in my case, which I wanted to use. But the case designers didn't, for some reason, expect it to be used. Even though there were holes drilled in the aluminum inner casing where the fan mounts, there were no openings in the colored plastic outer shell. So I dremeled some. The shell had some stylistic "arc" shapes in the plastic, so I just sliced big slots in those arcs with the dremel tool. Nice big openings for air, now. But when the fan was installed it still didn't blow much air because the holes in the aluminum inner shell were too small. So I dremeled ou that section of the case, slicing it up much like Archeon's picture. Now that fan blows plenty of air.

The second case fan was for the drive bays. I had enough room to squeak a single 80mm fan right in front of two of my disk drives. But the drive bay covers are solid, thus not able to transfer air. So I drilled a nice circular pattern of holes in the drive bay covers, and hot glued everything together as a unit. Now that fan blows a significant amount of air over the disk drives and keeps them cool.

So the system now has two 80mm fans blowing room-temp air into the case from the front. One at floor level and one at drive-bay level. There are ventilation grates in the back of the case which allow the air to exit out the back. The power supply also blows out the back. So I think I've now got it doing what I'd like it to do, airflow-wise.

The CPU idles in the 105-115f range now, and it didn't get any higher than 140f as I was playing through the rest of Unreal 2 today.

The only thing left is to re-arrange my disk drives and get rid of one of the three so that I can have only two disk drives with both of them being blown upon by the upper fan. Right now the C drive is between the two fans, right under the floppy disk drive. And it gets hotter than I'd like. So that's just a re-arrangement question I think, and then all will be well.

It's noisier than my old system, still, but I think it's about as quiet as I'm going to get it.

One final note: Those Zalman and Vantec fans are POWERFUL. First time I've actually yelped in pain when my finger accidentally hit a case fan.

Thanks, everyone, for all the helpful information and suggestions!