For standalone Windows XP machines in a workgroup environment, you can disable Run As by hacking the Registry. Simply use
Regedit.exe to locate the following key on each machine:
Then create a new DWORD value named
HideRunAsVerb and assign it a value of 1.
In a domain environment, you can disable RunAs using the Software Restriction Policies feature of Group Policy. To do this, open the appropriate GPO in the Group Policy Object Editor and locate the following node in the console tree:
Computer Configuration/Windows Settings/Security Settings/Software Restriction Policies
Right-click on this node and select New Software Restriction Policies, then right-click on Additional Rules and select New Path Rule. Now type the path to runas.exe and make sure the policy is set to disallowed.
If you prefer to apply this policy to specific users instead of computers, use a GPO linked to an OU where the user accounts reside and configuring Software Restriction Policies using User Configuration instead of Computer Configuration, such as:
User Configuration/Windows Settings/Security Settings/Software Restriction Policies