You want docs/DOC-3495

It probably won't work in core 4 since core 4 uses the formerly enterprise WMI pack.  You could however create a template with a WMI datasource and use the same query as the WMI Terminal Server ZenPack is using.  The query is in the screenshot on the ZenPack's page.

Using the Zenpack works just fine in 4.2 SP1. The ony thing I had to change was rename ZenPacks.community.WMIPerf_TerminalServer-2.1.egg file

Summary of installation:

As user zenoss (su zenoss) from root

wget servlet/JiveServlet/download/5913-13-9403/ZenPacks.community.SQLDataSource-2.4.egg.zip
wget servlet/JiveServlet/download/3392-30-7467/ZenPacks.community.WMIDataSource-3.0.egg.zip
wget servlet/JiveServlet/download/3495-8-3036/ZenPacks.community.WMIPerf_TerminalServer-2.1-py2.6.egg.zip

unzip ZenPacks.community.SQLDataSource-2.4.egg.zip
unzip ZenPacks.community.WMIDataSource-3.0.egg.zip
unzip ZenPacks.community.WMIPerf_TerminalServer-2.1-py2.6.egg.zip 
rm -f *.zip

mv ZenPacks.community.WMIPerf_TerminalServer-2.1-py2.6.egg ZenPacks.community.WMIPerf_TerminalServer-2.1.egg

zenpack --install ZenPacks.community.SQLDataSource-2.4.egg
zenoss restart
zenpack --install ZenPacks.community.WMIDataSource-3.0.egg
zenoss restart
zenpack --install ZenPacks.community.WMIPerf_TerminalServer-2.1.egg 
zenoss restart

Once installed, you'll need to configure zWinUser and zWinPassword with the appropriate credentials that can query WMI on your Windows box. Once set, Bind the WMITerminalServer2008 template to the device and assuming that everything is configured, you should start getting graph results in 10-20 minutes.