I recently re-installed Windows 7 and tonight I got round to installing Enemy Territory (ET), only to encounter issues with PunkBuster not running (despite being enabled in the game).
The fix was to manually install PunkBuster as follows:
Download and extract pbsetup.zip.
Run pbsetup.exe and click the Add a Game button. Select Enemy Territory from the drop down list and then Browse to the location where you installed ET. Then click the Add Game button followed by Check for Updates.
Download pbsvc.exe and run it to install the two PunkBuster Services.
This was enough to fix the issue for me – remember to run ET as an Administrator!