Will a remote release for a Nikon D90 camera work on a D40?

It's a birthday present for my dad, and I don't want to be getting him something that doesn't work on his camera.

If you're talking about the ML-L3 wireless remote control (which I have and love), YES, it will work.

If you're talking about the corded remote, MC-DC1, no, that won't work with the D40.