At this moment in time, the best average priced processor you can probably get is the Intel Core 2 Duo E6400 or E6600. I'd seriously recommend you DO NOT buy anything with Pentium in the name.
If you were looking for a laptop I'd honestly recommend a Macbook Pro with windows set as the default OS in bootcamp, but since your looking for a PC I'd recommend HP/Compaq or Dell, or to go the do it yourself route. Something like
this may tickle your fancy.
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