As a useful tip to those who might need to run ArcCatalog as a different user (i.e. a Network Administrator) this is how you do it with both Windows XP & 7 operating systems.
Windows XP: When ArcCatalog is docked on the taskbar, right click on the icon and the context menu will appear and choose run as a different user.
(ArcGIS 10) Windows 7: When ArcCatalog is pinned to your taskbar hold the *shift* key down and then right click and a context menu will appear with Run As Different User available. The normal right clicking still applies when navigating to ArcCatalog through the start-up menu.
Thanks to Leah & Susan R. from Esri for all of your help on this!
Erin