PC2100 and PC3200 will work together so you should not be having any problems with the system running slower then what it was before. The only downside to mixing the two speeds is PC3200 will slow down to PC2100 speeds. Which OS are you running? Have you updated the BIOS? The best way to install all the memory is to install the PC3200 in slot one, which is the one closest to the processor and then install the PC2100 in the remaining 2 slots. Let me know what happens when this is all done.
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