I found this online and a lot of people saying it works. Let me know if it it does, we can make it a sticky.
1. Install the game
2. Apply the official 1.3 patch
Code:
https://download.activision.com/callofduty2/CallofDuty2Patchv1_3.exe
3. Download the Fix
Code:
https://**********.com/files/10310235/CoD2MP_s.rar
or
https://**********.com/files/11489032/i-cod2m3.rar
4.Replace the CoD2MP_s.exe file in your CoD2 folder.
ENJOY ONLINE PLAY WITHOUT ORIGINAL CDKEY!
IT IS PUNKBUSTER SAFE !
You CAN play with this on esl or clanbase.