undetectable Keylogger?

[macattack1980]

I own a Mac Pro G5 and I am looking for a keylogger. Is there anything out there that is virtually undetectable to anyone else using the computer and won't cause any complications (freezing, etc..) after it has been downloaded.? Is there anything on the mac that would alert a user of the keylogger being downloaded?
One more thing, do cookies give me any information regarding computer use? My computer does not erase cookies.

Thanks everybody, in advance.