I'm pretty sure that the 915 chipset doesn't support dual-core cpus. The best you can upgrade to is something from the 600 series of pentium 4's. They have a 2MB cache and you can get something like a 650 that runs @ 3.4Ghz.
Hmm, with only 512MB of ram, i doubt a dual core CPU would really help you..
If i were in you, i'd get 1GB of ram, if you have free slots in the mobo..
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