Well, on your current machine I would wait, you won't full enjoy and appreciate this plane with your specs.
As for your new system, it depends on how much you are willing to spend. Make sure to get high end processor ( i7 if you can ), high end graphics card ( something like Geforce 260, 275,295 ) good amount of ram, and what's important, a good power supply. Something like a 750watt psu, with over 40 amps on the 12 volt rail.