I've used Micron (Crucial) memory since the 386 days. Currently I'm running Crucial Ballistix PC3200 (4) single sided 512MB (2GB total) on a "fully populated" MSI Neo2 mobo w/AMD64 3200+. It runs 2-2-2-6 1T with no problems. Now, here's the deal with Ballistics: a straight up online order will get you double sided modules, but you can ask (for the same $$$) for single sided, so in the future you can add two more and still run DDR200 at 1T. Double sided S-939 typically must run PC166 2T with four memory sticks used. Also, if you buy direct from Crucial you get a lifetime warranty and they will cross-ship if you have a problem requiring an RMA. As for buying PC4000 vs 3200, well Dude, Micron ... and everyone else ... uses the very same chips, just clocked slower!