After installing Wireshark 1.6.9 and trying to launch, I get "This application has failed to start because libxml2-2.dll was not found. Re-installing the application may fix this problem." A re-install does not resolve the issue. Re-installation of Wireshark 1.6.8 works fine.
This is an issue in the 1.6.9 build, 1.6.10 will be released to fix this. See this mailing list message for info, and you can download the 1.6.10 pre-release here.