Well, that is an AM2 Motherboard, and the Phenom II's are either AM2+ or AM3.
The fastest processor that I can find that would work with your motherboard would be the AMD Athlon 64 X2 6000+, I think
. It's out of stock @ Newegg at the moment, but you might be able to find it somewhere else.
It would be quicker, but it wouldnt match a Phenom II 955.