ok is what im thinking right: my computer has 128mb RAM. which i think means that it can have 128mb of stuff (programs sound files ect) RUNNING at once. now if i had a 129mb program and all of the things in it loaded at the same time to the full 129mb would the program either not work or would it mess up your computer? anyway i have never seen a program that large that loaded all files and stuff at once, but i guess its an interesting theory.

It depends on your OS. Windows uses harddisk space as ram when it is low on ram, a dos program would just not run when there's not enough ram, at least under dos.

Yep, Xception is right. You can notice it when your Hard-Disk is heavily used... But I have 512 MB 133 MHZ ddr ram... :P