If you get the Time Zone prompt every time you load Outlook 2007 and want to disable it, you'll need to edit the registry.

At the Start menu, Run command, type regedit.

Browse to
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Options\Calendar

Create a DWORD value "DisableTimeZoneAutoPrompt" and enter a value of 1

This will stop the Change Calendar Time Zone prompt from popping up automatically. If you change time zones, you'll need to run the time zone update utility yourself (Tools, Options, Calendar options, Time zone)