After this post...
http://www.vistax64.com/gaming/113654-no-replies-my-call-duty-4-problem-thread-question.html
...I was still being kicked by Punkbuster. I reinstalled twice, updated Punkbuster and ran pbsvc.exe without success. This is the one change I made that has allowed me to play COD 4 without getting kicked by PB. I right-clicked the multiplayer icon and checked the run as XP service pack 2 compatible under the compatibility tab. I even disconnected my router and "gasp" turned of the Vista firewall to eliminate anything that might have blocked my connecting. *I have since enabled both firewalls*. I have been running it on and off for 2 days now, no errors. Try this and please let me know if it works for you. Then other people will hopefully find this thread.
http://www.vistax64.com/gaming/113654-no-replies-my-call-duty-4-problem-thread-question.html
...I was still being kicked by Punkbuster. I reinstalled twice, updated Punkbuster and ran pbsvc.exe without success. This is the one change I made that has allowed me to play COD 4 without getting kicked by PB. I right-clicked the multiplayer icon and checked the run as XP service pack 2 compatible under the compatibility tab. I even disconnected my router and "gasp" turned of the Vista firewall to eliminate anything that might have blocked my connecting. *I have since enabled both firewalls*. I have been running it on and off for 2 days now, no errors. Try this and please let me know if it works for you. Then other people will hopefully find this thread.