It sometimes hangs on the initial MMX instruction test too.

I'm using a socket 7 TX Pro board. It's got a Cyrix 233 CPU in it. I ran memtest, just to see if there was something wrong with the RAM, but this test passed. Also, Windows 98 appears to be running smoothly, so no problems there either. Finally, I ran Everest Home edition (the free version), and clicked on quite a few things. Nothing bad happened.

Perhaps Speedsys doesn't like the Cyrix CPU?

PS - I doubt whether this makes a difference, but I'm using an ATX PSU, with my ATX to AT power converter gadget. I've plugged the power cable in to the old AT-style power socket on the mobo, rather than the newer ATX socket. (It's got both.) I did this, because I just couldn't be 100% sure which jumper-style pins were the power pins on the mobo, for me to poke a screwdriver at, to get the power started. I just didn't want to take the risk. So, I'm using the mobo's AT power socket, so that I can turn the power on using the AT power switch. The point I need to finally make here is that the Corsair ATX PSU that I'm using has no -5V rail.