you have 2 ways to overclock your cpu to 1500mhz, you can either increase the fsb or increase the multiplier
if you overclock with just increasing the multiplier then the rest of your system will stay right at spec, meaning nothing else is overclocked and any pc133 ram will work
if you overclock with increasing the fsb that will increase the speed your ram runs, and yes you will need higher quality ram depending on how much you want to overclock, just remember that its not just the ram, but when you overclock the fsb you are overclocking the agp and pci bus also, so you may have pci cards that are not capable of running on an overclocked bus, same with the hard drive.