it does depend on the motherboard - for a celly 466, it's socket 370, so it could be a 'relatively' modern chipset, supporting 100 and/or 133mhz front side bus (in which case any sdram at all should be fine).
If it's an older chipset then you would be better to look for 2 128mb (low density) sticks, or one 128mb and keep one of the 64mb sticks.
I'm not sure what you use the computer for, but windows 98 doesn't generally benefit too much from added ram much past 128mb; I doubt you would notice any difference at all between 192 and 256.