Don't raise it up to 220 as you will certainly fry your RAM. You want to raise the FSB in small increments of 3-5MHz at a time and then test the RAM with a program such as memtest86+ to make sure the RAM isn't erroring and running like it should. It'll be easy to explain it in this case since you have a 64bit system and the FSB in the BIOS will be at 200....Your memory is 400MHz and that is acquired through it being DDR meaning DOUBLE data rate, so that 200 that you see in the BIOS is 200x2 = 400Mhz PC3200...You want to loosen up your Cycle Time (Tras) when you go above 200 and this will allow you to overclock it because once you do overclock it so far you'll 100% guaranteed get errors in memtest86+ so my suggestion is:
Bump your FSB to 205...save settings and reboot with memtest86+ on a bootable CD or Floppy and make sure your boot sequence is set to the CD or Floppy first....if it passes all the tests then cool you're in the clear. If it doesn't...then try bumping up that Cycle Time (Tras) by one, save settings, restart and see if you still get that error. Generally it'll error on Test 5 when you're overclocking the RAM. You can only get so far by bumping up the Cycle Time however, which if you didn't know is the largest number in your timings IE XMS depending on which series of XMS is 2-3-2-6 so you'd want to raise that 6 to a 7 and it might get rid of the errors...
So if you're able to go up to 205 with no errors, then bump it up to 208 or 210 and repeat the processor, more than likely if you didn't get errors at 205 you definitely will once you get past that and you WILL have to loosen up that timing. Once you start hitting 215-220 not only will that Timing have to be at like 9 or 10, but you might have to bump up your Dimm Voltage by .1 to make it 2.7 instead of 2.6 since you have RAM heat spreaders you can probably hit 2.8 without fear of damaging your RAM but I warn you 2.8 voltage on the dimm is fairly high, but I hear the XMS is power hungry as it is. Hope this has been informative