It is a stretch to call it just a PC built from COTS hardware. The NV2A GPU was a modified version on the NV20 and included the Northbridge. The MCPX Southbridge was custom. The DVD was customized for anti-piracy. The CPU is a (slightly) customized PIII. If it was all COTS, the XBox XEmu emulator would be further along than it is now.