Recording a demo from within Call of Duty
Make sure the console is enabled in settings (options/game options/enable console)
Open the console using the "Tilde" key (the Tilde key is just below the Esc key)
to start recording type /record demoname
to stop recording type /stoprecord
if you give the demo a memorable name like the name of the player you are recording eg: /record RogerRabbit it will be easier to find on your hard drive. Give each demo a different name RR1 RR2 RR3 etc.
to review a demo open the console and type /demo demoname eg: /demo RogerRabbit and the demo will be replayed