I don't think the old pentium motherboards have softFSB. You might have to do it manually through jumpers, which I don't have any experience with (I distinctly remember something about jumper 11??). Back when I had my old Pentium 100 my friend came over and overclocked it to 120. That extra speed really helped for 3D gaming , but didn't do anything for Windows.
Most of mobo´s have their number(model) printed on it
its easy to find the manual over the net
i did this once, with my old pentium 233 MMX, the mobo was a asus, but i didnt have the manual, so i looked and found some numbers and letters
put this in a search engine like google or altavista
hope it helps