Windows 8 is still a restricted, incomplete and unreleased version of Windows. At this time Evenbalance have not incorporated support for the latest version of Windows which will result in errors such as the following when playing games that require Punkbuster whilst using Windows 8;
"Unknown Windows Api Function"
Currently there is no work around for this issue, it is likely that the situation will be similar to that of the Windows 7 release, in that Evenbalance will make no changes to Punkbuster to resolve the issue until the new version of Windows is ready for release.
For the time being the only workaround would be to reinstall Windows 7, or install Windows 7 to a separate partition specifically for playing games that require Punkbuster.