hey everyone: could any one tell me what is the difference between pc2100 and pc400? can they works together? does pc400 need special slot for the memory that different from pc2100 uses? thanks

The DDR slots is the same. I think voltages are also the same. So if your mainboard supports pc2100 memory it should also support PC3200 memory. The only difference is that DDR400 or PC3200 memory runs at 200 Mhz while 2100 memory runs at 133. But DDR400 can be downclocked to 133 I think without issues but I am not sure on that. As with video cards if you underclock them to much they get unstable for example. However CPU:s I have never seen that issue and don

i used to have an XP2200 with a 266fsb which would have been ok with 2100 memory but i had 3200 (512 to start with and then 1.5 gig) i had no problems running it at the lower speed, i now have a 333fsb but as i have a 400 ultra chipset so it matches the ram especially when/if i go for a 400fsb. it should work but you will allways be slowed to the lowest speed.you would therefore be wasting your money by getting 3200, much better to match the stuff you allready have.