Nearly any board should fit. Only thing is your tower isn't as tall as others so you'll need any mATX board. They are common however so this shouldn't be a problem.
You'll also need a board that has onboard video, or a video card. (GPU) Depending on the one you pick you might need a new PSU as well. And because the OS you have on there is looking for the gateway bios, you'll need a new copy of windows as well.