I think as long as both are 939, which they are
, you're fine. On Newegg, it doesn't list Opteron as one of the choices for my board, but I've heard of others using it and almost made the switch myself. You might want to wait for more confirmation, but I'm pretty sure it'll work.
You might also want to try overclocking your 3200+ if you're dissatisfied with performance, if you know a little about overclocking. It's strictly up to you, because you can damage some of your hardware in doing so. But I figured since you were on the verge of upgrading, why not give it a shot? You could probably make it up to 2.4 with ease, possibly up to 2.6-2.8 with a good stepping and cooling. 2.8GHz would tremendously improve performance if you could get there. And if you're not planning on overclocking the 3200+, I hope you're prepared to overclock the Opteron. I haven't heard of many cases where the 165s reach less than 2.7; they're quite possibly AMD's best overclocking chips. If you keep it at 1.8GHz, it may actually seem slower
than your 3200+ in some
instances. And if you do ultimately decide to overclock either processor, good luck!