|It would be better to have 2 x 2GB rather than 4 x 1GB plus you should be more concerned about running the optimal CPU:DRAM frequency ratio rather than trying to run the RAM as fast as you can. The two ratios that are considered optimal for an Intel system are 1:1 & 1:2.|
If you run your CPU at it's deafult frequency of 333MHz (1333MHz FSB), you should run the RAM frequency at 333MHz (DDR667) for 1:1 ratio. For 1:2 ratio, the RAM should be run at 667MHz frequency (DDR1333).
To take full advantage of DDR2000, you'd have to overclock the CPU frequency from 333MHz (1333MHz FSB) to 500MHz (2000MHz FSB). That would require changes to several BIOS settings (multiplier, voltages, etc) to be able to pull it off, IF you're able to pull it off at all.