this is probbably simple but i put an old video card from another pc into mine ( i have 2000 pro as an os) I can get that card and the monitor installed to work fine but it disables the original monitor on the mother board.

pulling the card makes the original work again whats up...is it some kind of jumper or a memory allocation thing??

You'll have to get a card that supports dual-head. You can't have an onboard device and an external device work at the same time, that's a safety feature that the BIOS disables the onboard once an external one is plugged in.

is there a possibility of disabling the security feature that disables the onboard?

Nope.