System clock runs fast, keyboard rrrrrrrrrepeats

[Squishy]

I've recently set up an old Pentium P54C, 120 MHz computer to run OpenBSD. The keyboard goes crazy at random times, repeating a single (quick!) keystroke about ten times. The system clock is also running very quickly, probably around five times quicker than it should. I've checked the motherboard and PSU, cleaned all the contacts, and tried reinstalling with minimal components and default options. The keyboard issue seems to come up when X is started. On searching for similar issues, I keep coming across suggestions to boot with "notsc divider=10" with no explanation on how to do it. Is this something to be done with the config utility? I'd like to avoid recompiling the kernel because the computer is so slow and I've never done it before.