No, buffered RAM is not the same as ECC.
ECC is error correction -- it enables the memory to automatically correct single-bit errors and detect multiple bit errors.
Buffering puts a buffer chip on each memory module, so the module presents one load to the address and data bus instead of one load per chip (typically 16 loads per module. This lets you use a LOT more memory without causing signal degradation on the bus. I NEVER install more than two memory modules in unbuffered systems -- which keeps the memory subsystem much more reliable.
The Precision 3400 uses standard unbuffered DDR2 memory, but does support ECC modules - which I would use. The 5400 has fully buffered DIMMs with ECC ... these are much better => but in a system that's just going to be running 32-bit XP and not have more than two installed modules, a pair of ECC modules with a Q9550 in a Precision 3400 would be a fine choice, and is clearly more economical.
