Personally, I would just go and get PC3200 RAM. It's very readily available, and often times cheaper than lower speed RAM. Also, if you end up upgrading later, it might save you one thing to upgrade.
Don't get confused with ECC or buffered RAM. All you need to look for is non-ECC/unbuffered RAM.
When the bus runs at 100MHz, lets say, that doesnt mean you run PC100 RAM. Read my RAM Guide for some help with that
For example, this RAM would work fine for you:
Just to clarify, if you put PC3200 in a system that only supports PC2700, the RAM will run at PC2700 speeds by default, but will still work.