How is your memory configured. To properly run in daul channel mode the memory is required to be the same.
If you are running one memory module (1 gig) and a second Memory module (2 gigs), 2 things -
1) the speed will be the slower of the two, and
2) YOU are running in single channel mode, NOT daul channel. Single channel is MUCH slower.
You can down load CPU-z (google it). install and run.
Look at the top. click on memory tab and look to see if single channel or daul channel mode.
The SPD tab shows what the memory is capable of running at.
Your CPU is not at full capability according to that page.
(Note) If you install AMD AM3/ AM2+ CPU on AM2 motherboard, the system bus speed will downgrade from HT3.0 (5200MT/s) to HT1.0 (2000 MT/s) spec; however, the frequency of AM3/ AM2+ CPU will not be impacted. Please refer "CPU Support List" for more information.
How did you verify You are in daul channel mode, did you run cpuid CPU-z? http://www.cpuid.com/softwares/cpu-z.html
When you run it click on Memory tab at top. That will show you what the ram is running at and if in sngle/daul mode.
Not an expert on amd chipsets, But with INTEL, you can not run in daul channel mode with two different sized modules.
..DDR means that data will be transfered on both the leading edge and the lagging edge. This is NO problem.
..The 2 means that the memory will operate in parallel mode. Halve of the 2 gig model does NOT have a corresponding parallel memory in the 1 gig module so can not be in daul mode.