Here is a vb script that does the trick....
Just copy this into a text file and rename the extension to .vbs (oh, and make sure some of the lines don't wrap)
ComputerName = "COMPUTERNAME"
winmgmt1 = "winmgmts:{impersonationLevel=impersonate}!//"& COMPUTERNAME &""
Set UserSet = GetObject( winmgmt1 ).InstancesOf ("Win32_ComputerSystem"

strCurrentUser = ""
cntrs = 0
for each User in UserSet
If cntrs > 1 Then
strCurrentUser = strCurrentUser & ", " & User.UserName
Else
strCurrentUser = User.UserName
End If
cntrs = cntrs + 1
Next
Msgbox "Current Logon (" & COMPUTERNAME & " is " & strCurrentUser, vbOkOnly, "Current Logon"