Turn off UAC. CS3 was never developed or tested on Win 7 and this may be mundane compatibility issues.
Also check in the new user account , does it work fine there.
CS3 may or may not work on Win 7 machine as it was not tested on win 7. You may try uninsalling MC CS3 and then re-installing it on a new user account and check if that makes any difference.
Turn off User Account Control as well : http://helpx.adobe.com/x-productkb/global/disable-user-account-control-uac.html
Restart Windows in a modified mode | Windows 7, Vista - http://helpx.adobe.com/x-productkb/global/restart-windows-modified-mode-windows.html