MIDI confusion

Okay, at the risk of sounding like a total moron, I guess the thing I'm having the most trouble understanding is MIDI. I kinda understand what it is and its purpose, but how I can use it is bugging me. I've seen lots of different MIDI cotrollers, and I guess thats whats cofusing me. If I buy a drum machine for instance, will I be able to connect that to my computer and access, or control the drum sounds in MC4? Recording drums is my main concern at this point, and I would like to have the freedom to "play" the drums, and not just use some preset drum sounds. Would I be better off to buy a controller with a keyboard? It seems that would be a lot more versatile, as I could actually use piano type sounds. The more I think about this, the more unsure I am. Any suggestions?

Understanding midi take all the fight out of these decisions. Midi is a universal machine language designed to tell a sampler, or synth program or hardware box what notes to play, and how. Example you have a drum machine with midi in and out, inside this box you have a set of sampled drum sounds, or small recordings of drum sounds. The midi data either from a sequencer like MC, or a keyboard of from the pads on the drum machine, and this will tell the sample program which drums sounds to play and in what order and at what volume and velocity. that signal goes out in two ways 1.) Thru the midi port as data only which can be used to fire or trigger any other synth or sampler, or to be recorded inside a program like MC as midi data, recorded in a MIDI track. 2.) Out thru the audio jack as sampled sound, which can be recorded as wave file in an audio track.