Definitely time to upgrade your motherboard as well. Socket 939 is going out fast. Even the AM2 has hit the end of it's road stopping at the 6400+. The only thing that will keep the AM2 alive is the fact that AM2+ boards support the quad core as well as the dual core processors.
If I were you I would go with the GIGABYTE GA-MA790FX-DQ6 or similar and a AMD Phenom X4 9600 Quad Core Processor.
I will be upgrading to that board soon, but I might wait for better quad core processors to be released by AMD. I certainly dont have anything against Intel as I was using a P4 on an AGP board up until about a year ago, but I think AMD will crush Intel soon with new Quad Cores.
And yes, they are true Quad Cores.