Hmm, I think you shouldn't be too bad off, I don't think.
I've got the following system, and I had no real trouble, aside from a slowdown to about 20fps or so, after jumping a 100-ship fleet into a pirate planet with ~800 pirate ships in it. And lost only *thinks* 25 ships, in the course of obliterating the pirate presence in that solar system.
AMD Athalon 64 Dual Core 4000+ 2.11 GHz
256mb GeForce 8600 GT
2 GB ram
Vista 32bit
And I run it with everything maxed out, with x2 AA. Sins is very friendly with older hardware.