Dude. Am running Vista on a 2Gb ram and a 2yr old 2.3GHz single core processor.
your vista should run without a hiccup.
But, before you upgrade,run Vista upgrade advisor to check if your h/w has proper drivers for Vista.
By your siggy, it should be fine.
Vista 32-bit should run fine on 4gig ram but only 3.5gig will be recognized.