I got an A4000/040 and it has this weird key place on the front. The person I bought this from didn't include the key thing and I want to know what this does. Will not having the key disable functions of my computer?
It is a generic keyboard lock key. If your keyboard works, your good! Anyone who had a A4000 that I knew never used the key and usually lost them!

As for trying it out while not haveing a keyboard... Well, you could find a generic BIG-din to PS/2 style adapter and plug in the A2000 KB you have... Heck, find an old KVM switch and your set!