Permissions and 64bit IE will be most likely your culprits. here's what I've found that works within my company.
As Dan mentioned, make sure you turn UAC off during this process.
Run the ALMUninstaller to clean up any existing instances. If you've already uninstalled through Windows uninstaller, you probably won't pick anything up. Just re-install the client and then re-run the ALMUninstaller. It works like CCLeaner does but focuses on ALM.
Clean up any residual folders that may still be lingering (generally at C:Program Files (x86)Common FilesHPHP ALM Explorer 11)
Reboot
When you log back in, open a command prompt as administrator (Click the start button and enter CMD in the search bar. When it comes up right click and select ''Run as administrator''.) I've found doing this through the command window seems to help get around some oddball security measures vs. doing the ''right click run as'' option.
In the command window, navigate to where your installer is and execute it.
Upon completion of the install, got to the install directory (C:Program Files (x86)Common FilesHP) right click on it and select the ''Security'' tab. Add the ''Everyone'' user account and grant it along with the ''User'' account modify permissions.
launch the 32bit version of IE (C:Program Files (x86)Internet Exploreriexplorer.exe) by right clicking and selecting ''Run as Administrator''.
Enter in your ALM applications URL and the files should download. If you're using say v11.x, you'll need to go to http://yourhpinstance/qcbin/start_a.jsp?common=true which will register the files.
Go back tot he ALM Client app and open it, enter in your ALM URL and it will perform the same.
Turn UAC back on and restart your PC. Test it our after it comes back up and you should be good to go.
Hope that helps!
Steve