Hi pthomas, I had this same issue. What worked for me was:
*right-click on the UDKInstall-2012-03-BETA.exe and select Properties.
*Go to the Compatibility tab and click on the button "Change settings for all users".
*In the window that pops up change the drop-down under Compatibility mode to your version of Windows (ex. Windows 7).
*Make sure there is a check-mark next to "Run this program in compatibility mode for:"
*Click the Apply button for this window, then click the OK button for both windows to close them.
*Try the install again.