From MSTS:
To turn off the Windows Update feature, follow these steps:
Click Start, click Run, type regedit in the Open box, and then click OK.
Locate the following registry subkey:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options.
Right-click Image File Execution Options, point to New, and then click Key.
Type wupdmgr.exe to name the new subkey.
Right-click wupdmgr.exe, point to New, and then click String Value.
Type Debugger to name the new string value.
Double-click Debugger, type ntsd -- in the Value date box, and then click OK
Although, I did have them kill it two or 3 additional times after this procedure.