Oh, cool, a potential Cyrix MediaGX1 build! I haven't run into anyone from Vogons running the GX1. I run the GXm-266 (PGA form). I sourced a rather hard to find GX1-300 in PGA form, but it didn't run well in my motherboard. My board has the CX5530 chipset and, until I saw your motherboard photo, thought that the GX1 could only work with the CX5530A chipset (based on what is written in wiki).
On my motherboard, I recall needing to disable the onboard video in the BIOS to use a PCI card; either that, or I had to set the VGA priority. However, part of the historical glory in using MediaGX motherboards is because of the novel way in which Cyrix integrated the memory congroller, graphics, and audio into the CPU. They were way ahead of their time. But alas, I also run my system with expansion cards because the onboard graphics and audio are pretty bad when compared to the alternatives. I use a Banshee in my board.
Also interesting about your board are the 3 PCI slots. I recall the MediaGX being limited to 2.
I also like how your board has 72-pin SIMM slots. Mine only has two SDRAM slots. I wanted to use 256 MB of RAM, but for stability, I would need to add a memory timing wait-state. To eliminate that wait-state, I instead use 192 MB. I've run into this issue on other socket 7 motherboards which contained, both, SIMMs and SDRAM slots and using the SIMMs, rather than SDRAM, allowed for less wait states.
I use PC100 in my board just fine.
The manual mentions it has a PS/2 mouse header!
Did you setup all the jumpers accordingly, like 33 or 30 MHz FSB, correct multiplier, CPU voltage, etc? There is even a jumper to set your memory voltage, 3.3 V or 5 V. I wish my board had that feature. I have some 3.3 V SIMMs which no other board I own can use.
Plan your life wisely, you'll be dead before you know it.
