I noticed you said that they are masking their machine name or user name when they are net sending. It is possible that they are using a 3rd party tool, such as the one that people are currently using to send direct ads using an exploit in the messenger service. You may want to look into limiting what executables the users can run on their systems. This can be done using GPO's. If they are definelty masking their net sends, then this just might be the case. I know for a fact that there are multiple cracked versions of this software out there, and in the hands of some user it could definetly cause a lot of hassle. You may want to look into what exactly is out there on your network.
also...you can use a one time login script using the run as command tostop the service and change it to manual startup under the administrator context if you do not want to go the route of putting users into the local admin group. Although, with GPO's, you can add all the users to groups and then add those groups to the local admin group. This gives you the option of setting some serious restrictions on what those groups can do. This allows you to have them process scripts that require administrative priveledges while giving you the ability to lock down other administrative rights.
JPGregg
Network Administrator
A+, Network+, Internet+,
MCP, MCSA