ECS K7SEM is the only thing that comes to mind. I've used them before. No frills but it has onboard video, lan, audio. PC100/133 memory, micro-ATX board. (2 PCI slots) The only concern I would have is that statement on ECS's website:
We had verified and confirmed that K7SEM can be guaranteed to support 100MHz AMD CPU and the MAJORITY OF THE 133MHz CPUs.
The two I've built used 900 Durons.