yeah that cpu is holding you back big time.
Your motherboard can take a phenom II x4 970 or x6 1100t (with the most recent bios) and would be a great upgrade from that phenom (1st gen) 9600.
That would be a cheap upgrade that would make your system pretty effective at gaming.
Not too sure if DDR2 mem would impact those cpu much but I'm thinking it won't be big deal. (maybe others can provide better feedback there)
Or you could always do a bigger refresh and go for a new mobo/cpu/ram trio. If you do, I'd go with intel 2500k/2600k (if you plan to overclock these 2 have unlocked multi and should see 4.5ghz and over quite easily) or the non "k" version which are locked if you dont wanna overclock.
This option would give you a better gaming rig for sure but will likely triple the cost of the upgrade ...