well there ya go...just slowly move the clock and mem frequencies up and see what your busting point it, I recommend using powerstrip to do it as it is easier to reboot and change the setting should they fail
oh and just to let you know...no increase you do is going to give you a major performance increase as in the chips just aren't made to be as highly clocked as a full geforce sorry man
it is the front side bus speed of your motherboard...it will boost your cpu's clock speed and everything else, but it is only really a speed boost for the cpu, upping the FSB itself does not directly help your video board or any pci cards, it mainly the performance of the proc increasing that your seeing
It depends what kind of motherboard and processor you got. I have a Celeron 400mhz and a Tekram i440BX-A motherboard, all I did was change a jumper setting on the processor and then in the system BIOS I changed a frequency setting (can't remember the exact switch).
As far as the GeForce2 MX400, I recommend a program called NVMax for that. I have my core/memory set to 240/350.
It's all trial and error, just make sure you have good cooling (or a good house fan, which is what I use).
Forgot to add, I have my Celeron set at 500mhz now, but you got to make sure you have adquate cooling.