Based on the processor and age I'd say it's most likely a 939, but you can verify that by downloading/running the free program Everest. Look under Motherboard->Motherboard->Motherboard Physical Info. Once you verify the socket type I'd check out what's available through newegg.com...they have a nice selection at fairly low prices and are quite reliable.
Honestly your temps sound fine to me, and a new heatsink/fan likely won't produce much of a change, but it's up to you.
Hope this helps,
How can I tell what socket I have. I would like to replace the stock cpu cooler that is on the system. I have an Emachines T6524 200gig hard drive/2 gigs of ram/AMD Athlon 64 3500+ I did have the PNY 7600 GS 256mb but it ran to hot...80c at idel and 100c+ at gameplay. I replaced the PNY for the Biostar 7600 GS 512mb and the difference between the two cards was like night and day. The Biostar 7600 GS is running at 45c at idel and 49c-50c during gameplay.The ambieant heat in my case is at 39c, the hard drive is at 34c, and the CPU is at 35c. I believe I'm in the market for a heatsink and fan combo any suggestions.