What motherboard are you trying to use? I formerly had a T5500 installed in an aOpen mobo (can't remember the model number) that made a great server (I used as a desktop for a while too and it was very good there as well). It was quiet and fairly capable.
You should be fine with either FSB speed as the mobo will adjust as needed. When you install the memory and CPU, the auto settings will adjust for the least common denominator (in most cases automatically) to account for differences.
Last, make sure your mobo includes a heatsink/fan for the CPU. You typically can't use a "regular" HSF with mobile processors (different dimensions).
Good luck! BTW, I am an AMD fanboy myself and my old system (died from an electrical problem) was a project similar to yours.