SW does not in general utilize a dual processor. FrodoWorks does. The only thing I can think of that this setup might help with is to run SW on one processor and PDMWorks on the other. But then you will run into RAM issues because until SW runs under XP64 you will be limited to the
3Gb. If you vault is so large that running PDMWorks on such a fast processor make sense it will limit your available RAM for SW. Catch22.
If you are planning for the future, put in a dual capable mobo but with a single Opteron 286 or better. Then when XP64 comes out and assuming you can get your hands on it get the second CPU or more RAM. Tyan makes some nice dual capable mobos that will hold much more RAM than the current crop of high performance single CPU boards.
I think there was one post a while back using the Dual gaming cards in SLI mode. He was just a squeak faster than my AMD64 FX53 with FX3000. So the FX3000 or similar CAD rated graphics card might make more sense.