AKM880 :
I don't think in my Dell case there is good airflow, I'll probably have to mod it and stick a fan off the side. Anyways do you think this case will fit ATX motherboards? How is overclocking on m-ATX boards? I see that you've ran two instances of Prime95, is it not optimized for dual/triple/quad cores?
I stuck another fan under the front cover of the Dell to increase airflow, it normally only comes with one rear exhaust fan. With that extra fan in the front it ran pretty well and didn't get too hot at all. Got up to 64C once on a pretty hot day while I was running Prime95, which is a very managable temp and would have some longevity for the chip.
I couldn't find anything on Dell B1100...is that the same thing as a Dell Dimension 1100? If it is, it looks like it uses the exact same case that the Dimension 4600 uses, and no, it will not fit a full sized ATX board in it, you will have to use mATX. Overclocking can be good on mATX boards, it just depends on which one you get. The DFI LP Jr P45 board is supposed to have excellent OC'ing. The SBM this month used a ASRock G41 MB that oc'd to 4ghz with an E5200. The particular board I got wasn't particularly impressive, but it overclocked alright, as long as the IGP was disabled. If you were to get a Phenom II processor, Biostar makes a mATX 790GX board which overclocks well, as does DFI.
Prime95 only ran 2 threads in my build because I used a dual core CPU, but if I used an i7 then it would have run 8 threads if HT was enabled. Prime95 only runs as many test cores as your CPU has.