Your's will do just fine.
I play large maps on this (though I have to turn the graphics down for LAN or Internet games to prevent lag):
Dual Core AMD Opteron Processor 180 2.41 GHz
1 GB RAM
256 MB Nvidia GeForce 7600GT (GT or GTS; can't remember)
160 GB hardrive
Windows XP Pro
So far, I've found that aboul all I have to do is keep the planets' graphics on medium or low and pretty much no lag. (everything else at highest) And yes, I've played multi-sytem maps online, so your's will definately work well.