Just create your user groups in the Linux PDC and add the users to the groups. This is it.
Remember that the example scripts in this howto will probably fail if you have users belonging to more than one group. If you need this, remember to adjust the scripts.
You will need to define group specific scripts and place them in the directory "/etc/smbgate/groups/". Remember that the script must be named as the group, at least if you want to follow the examples in this howto.
The default scheme of this howto is to check for a user script, then for a group script and finally for the default script. If you want to modify this behavior remember to adapt the netlogon.sh, netlogoff.sh (or the checklogout.sh) scripts. The whole logic is in these scripts.