dont change the procesor yes you wil see an improvment becuase games only use single core but the new half life game will utilzes 2+ and this is set to carry on so best stick with what you have.
also with the mobo i wouldnt change as 939 is out and it would be a waste
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AMD 3700+ | A8N-SLI SE | Mid R600 | PC4000 Ballistix