You'd get much better information if you could identify the mainboard.
(Sisoft Sandra might help.)
For example: I ran a Slot 1, 133 MHz FSB 1 GHz PIII (7.5X133, Coppermine) on
a BX board (Soyo 6BA+IV). The 133 MHz FSB wasn't approved by Intel, but the
board included memory dividers so that everything except for the AGP slot
was run within specifications. (The graphics card, a Geforce 4 ti 4200, was
stable with the AGP slot at 89 MHz.) There was also a 100 MHz FSB 1 GHz PIII
(10X100), which would run without overclocking on some 440BX boards.
Note that there are at least two Slot 1 CPU retention mechanisms. The SECC2
one for the newer CPUs is quite different from the original one, and isn't
really compatible with it. (The retention brackets can be swapped out, if
you can come up with one.) I don't recall which version the PIII 500 was
most likely to use.
That leaves off the newer CPUs that could be used with a Socket 370 to Slot
1 adapter ("slotket").
Don't spend too much time or money on this.
Address scrambled. Replace nkbob with bobkn.