There is problem in vista home premium, you can’t load local group snap in MMC console. And it’s very cheap from microsoft
to remote the facility to control user groups from vista home premium, but there is way to manage groups using command prompt.
step 1 : goto command prompt and type
it will show you list of all groups on local machine.
step 2: to add user to any particular group use the following command
net localgroup [group name] [user name] /add
i.e. net localgroup administrators admin /all
find more about it in following forum.