You can find the bios here...
Look under the GeForce3 section, then ti200, then Nvidia reference bios.. Or something like that..
And yes, it should work with the 128mb card.. Just backup your old bios before you even consider flashing. Also boot with a boot disk into dos before you flash.
But, if you have Win98, you are in luck. There is a resident driver that you can load in the autoexec.bat that will load the bios into your memory, no flashing or anything, and when you turn off the computer, it is deloaded. So, it's perfectly safe (it's what I use).