well, for one it had to be said, there is seriously NO POINT in overclocking your pentium 75. It's not made for overclocking, and i doubt your cooling system is capable of handling the heat it will dish out.
If you havent got a fan on your heatsink, don't overclock it unless your just playing,
it WILL die. If it does have a fan on your heatsink, you may get away with it running at around ~90mhz, but only with a bit of good luck. Running at 120mhz, your chip would have a maximum lifetime of 2 days i'd say. With a chip like that, i wouldnt recommend overclocking it anything more than 5mhz extra, in which there is seriously no point in wasting your time.
Anyway, find out the make of your mobo, and the model number, and look for information on which jumpers do what on the internet. There are normally two ways, one would be to look for your mobo model written on the mobo itself, normally near one of the sides, with some FCC and CE information, etc. If it doesnt say on your mobo (some oldies don't), then when you first turn on your PC, and it starts to perform the POST, look near the bottom of your screen, it may say the model number. If it does, press pause/break on your keyboard which should stop the POST, and you can write the info down on some paper, then look on the net.
The only other way would be to the idea the winch came up with, and to go around the board playing with jumpers. The problem is, there are alot of jumpers (especially on old mobos), which if on the wrong setting, could just kill your mobo and sometimes everything attatched to it (it's funny when you blow everything up at the same time, changing some weired setting to make everything go with a bang- yes i once got bored and found an old i286 in my cupboard). If you resort to this tactic, i'd recommend first changing the nearest jumper to your chip. If thats not the one, then try the jumper nearest to the PSU > Mobo connection.
But be carefull, old things break easy.
TMB - under construction
Sticking feathers up your butt doesn't make you a chicken.