Uh, tough one, I've never had issues installing BSD on any hardware that I had and still have. My suggestions :
try different machine - same disk
try latest bsd - 7.0 on the first machine.
try looking at BIOS options at boot time, something could have gone wrong.
Last question - is this going to be server ? Because if it's intended for GUI with KDE for example, you can try PCBSD - PC-BSD - Home - it's a clone of FreeBSD 6.2