How to enable and use the "Run As" feature in Windows Server 2003

Enable the Secondary Logon Service

By default, the Secondary Logon service starts automatically when you start Windows. However, an administrator can disable the service. To enable the service if it is disabled:
Log on as Administrator or as a member of the Administrators group.
Click Start, point to Administrative Tools, and then click Computer Management.
Expand Services and Applications, and then click Services.
In the right pane, right-click Secondary Logon, and then click Properties.
Click the General tab.
In the Startup type box, click Automatic, and then click Start under Service status.
Click OK, and then close the Computer Management window.
Use Run As to Start a Program as Another User

To use the "Run as" feature to start a program as another user:
Locate the program that you want to start in Windows Explorer, the Microsoft Management Console (MMC), or Control Panel.
Press and hold down the SHIFT key while you right-click the .exe file or icon for the program, and then click Run as.
Click The following user.
In the User name and Password boxes, type the user name and password of the user whose credentials you want to use to run the program, and then click OK.
NOTE: You can also use the runas command from a command prompt. For more information, click Start, and then click Run. In the Open box, type cmd, and then click OK. At the command prompt, type runas /?, and then press ENTER.