when you say you exceeded max ram, what is the source of this limit? (i.e.: is this a limit you received from the motherboard, or software.) If this is a limit stated in hardware (for example, i815 based motherboards are limited to 512MB of ram), going over the limit will (1: probably not register the excess properly; 2: result in system instability; 3: run more slowly)
I would recommend that you remove the PC100 stick. If you are using 256 MB of ram with win2k, you should have plenty (unless you are using professional cad/cam, and several other types of really expensive professional software that ask for insane amounts of memory)