1. Which CPU? (I was thinking wolfdale for lower heat)
2. which motherboard? (it has to be ATX)
3. Which HSF? (Is there a smaller one than stock on the market that works well?)
1. CPU either a E8400 or the Xeon 3110(same as a E8400 but with the Xeon name).
2. Asus P5K-E WiFi/AP. Great mobo and supports every 45nm CPU out there. I have it and love it.
3. HSF is hard. But this one is a good one http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Now its not very high but is very wide. But it will keep it cool in that tight case.