You should specify what motherboard (brand+model) you have for us to know.
Is it a custom build or a name brand computer with that single core CPU?
If you know the motherboard again people here will be able to possibly help you out.
Yeah if it's a AM2+ motherboard (likely) the OP could possibly upgrade to 2,3,4 core AM3 Athlon II's or Phenom II's or even a 6 core Phenom II with a possible BIOS update.Again that's just a possibility.Some retailers online still sell the older Athlon X2's,Phenom X3,X4's too if you have an older board with no new BIOS CPU updates available.
That 65nm CPU was released in 2008 http://en.wikipedia.org/wiki/List_of_AMD_Athlon_64_micr...
It is possible that he could have the older AM2 motherboard as well but since the CPU likely was released in the midst of 2008 an AM2+ type motherboard would be the more likely possibility.