Slow PC – memory issues ?

My PC (PIII running on W98SE, motherboard Intel CA810E AAA01988-310) appears to be running slowly, and ‘clogs up’ once you have a few programs running. Belarc advisor gives the memory as Slot ‘DIMM1’ has 128 MB, Slot ‘DIMM2’ has 32 MB, which seems a little odd as I thought I had 256Mb of meory. Has one of the chips ‘partially’ failed, if that’s possible, or should I be looking in other directions to solve the perceived problem ?