HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\VBAWarnings=1 (REG_DWORD) is the setting you're looking for. It can also exist under HKLM as a machine-wide override. The location alos varies by office version; 2003=11.0; 2007=12.0.
Lastly, if you are in a managed IT environment, keep in mind that group policy may be changing it back for you.
JohnW
2009-03-09 13:13:10