Outlook 2010 uses Bing maps to map address but you can change it to other popular mapping services by editing the registry.

Open the registry editor and browse to
HKEY_CURRENT_USER\Software\Microsoft\ Office\14.0\Outlook\Options\General

Right click and choose New, String Value. Enter MapScriptURL for the string value name. Double click on the MapScriptURL key to open it and enter http://maps.google.com/?q=<0s >, <1s>, <2s>, <3s>, <4s> or the URL for another mapping service. Open a contact and click the Map It button to text. (You do not need to restart Outlook.)

You can also use this with Outlook 2000 and 2002, but not with Outlook 2003 or 2007.

See Customize Outlook's Map Link for more information, URLs for other map services and ready to use registry files to make the changes.
http://www.outlook-tips.net/howto/displaymap.htm