From what i can see, you're right. The Socket A Sempron 3300+ is just a rebadged Athlon 3200+ but with half it's L2 cache disabled.
I'm not sure how much of a performance increase (if any) you'll see, but the only way to find out is to try it. You should be able to swap CPUs without any major software hassles, just try something like Super Pi Mod with each processor and see wihc one is quicker...
Oh, and whichever one you don't use, I'll be happy to take off you're hands.
Don't ask questions, just click my rep tick. Now.