Ahh i played defrag in quake 3! I was never very good though. It doesnt look easy, but its still a billion times harder than it looks lol. You have to move the mouse the perfect amount at the perfect speed, you have to move the keys at the perfect time and hold them for the right length, you have to time each jump perfectly, and all the different jumps requires a different timing/speed for all those things. And then some of the maps require plasma climbing & rocket jumps and overbounce and all that advanced stuff =P Most of the maps on defrag i cant even complete, let alone do it with the crazy speed that some of the pros do it. My favorite vid is this:
Also, zagibu, its just a mod for quake 3, which came out in 1999 i think, so it isnt intensive on your pc at all. Thats one of the reasons i played it haha, my old pc couldnt run hardly anything. Its a lot of fun though.