Do you want the best or the quickest? The Best, follow the support notes. The quickest depending on your situation......
take the sylink.xml file from a managed client that is in the group that you want your new client to be in.
Stop smc.exe on your unmanaged client.
Rename the current sylink.xml, rename the sylink.bak
drop the sylink.xml from the managed client on
Start smc.exe
It will have the ip address of the management server and the preferred group populated to tell it where to report and where it wants to belong. Then it registers.