All RAM is not equal...
Always check out the CAS values for the RAM you are buying - most "value" options will be CAS 5-x-x-x. The first of the 4 numbers is the most important, as that is the number of clock cycles (at the specified RAM speed) that it takes to get the first bit moving in each request. You want to be getting CAS 2-x-x-x in whatever speed RAM you buy.
PC2100 is 133Mhz or 7.5 nano-seconds per clock cycle
PC2700 is 166Mhz or 6ns
PC3200 is 200Mhz or 5ns
Multiply the time per cycle by the CAS latency number to get the total time before your information is moving for each request, and you can easily see that it can be a big difference between CAS2 and 5 - especially if using PC2100.
I would check with ASUS tech support, but I think the A7V8X can support 1Gb of PC3200 if it's a single module, or 2Gb of PC2700 in

1Gb modules - in which case, the 2Gb low CAS PC2700 is the way to go.