What FSB speed are you using? PC2100 is only rated for 133 FSB, but PC3200 is rated for 200 FSB. I've seen plenty of PC2700 run at PC3200 speeds, but it's a little rarer that PC2100 will run at PC3200 speed. On the other hand, if the PC2100 will do at least 166 FSB, then maybe they would be ok together.