Octopus Overlords

I'm looking to upgrade my RAM and right now I'm running an XP2600+ with a 333Mhz FSB. My mobo (ASUS A7N8X-E Deluxe) supports up to a 400Mhz FSB and I may want to upgrade my CPU in the near future as well.

I know the RAM should be synched with the FSB so PC2700 would be the way to go now but I don't want to upgrade the RAM again if/when I upgrade the CPU. I noticed that my bios has a setting for memory frequency that will allow me to scale it to a percentage of the FSB frequency. Could I use this to slow the memory down and keep things synched if I went ahead and upgraded to PC3200 memory now?

Yes. The PC3200 memory is rated to work at the faster speed, but it'll work fine at the slower. Your motherboard should automatically run it at the speed your system best utilizes for your CPU, so you normally shouldn't need to make any manual changes.