Here is a list of processors
your board will take. The biggest problem is finding one and how much of an upgrade will it be? Those CPU's are difficult to find. I suspect, even if you found one, it would not be much of an upgrade for you. I would suggest you upgrade your board to a more modern chipset, new processor and ram. I know it would make it more expensive, but it would be a real upgrade that you will notice.
Also, here is a list of all LGA775 CPU's
at Newegg. I don't think any of them are compatible with your boaed.