from:
http://clanbase.ggl.com/doc.php?did=174&lid=5715#cod4
Step 1: Connect to a PunkBuster-enabled CoD4 server.
Step 2: Open your console (by default the ` key - otherwise check your control settings) AND holding down the Shift key at the same time.
Step 3: Type
/pb_myguid into the console window (full 32-digit GUID) or
/pb_plist for the final 8-digit GUID you need to register.
Step 4: Your CoD4 PunkBuster GUID will be shown, it is the key with GUID= in front. For example, the CoD4 PB GUID on this screenshot ends with
a0da237c.
If you don't see it, then you might have to scroll down to see your GUID. The PageDown and scrollwheel can be used for this.
To copy the GUID, write it down or better: make a picture. PrintScreen should work.
Step 5: Enter the last 8 digits of your CoD4 PB GUID on ClanBase on your
guid properties page.