LDAP Group assign to vlan after AD user authentication

Hi, I've successfully set up a radius server to support 802.1x authentication using peap mschapv2 and samba to authenticate users against AD. To do this I followed configuration on the freeradius.org website and the AD integration howto on deployingradius.com, thank you very much for writing these! I now need to assign the vlan due to membership of some group in AD and I understand that an ldap lookup is needed. Where in the configuration do I check this group and map it to a vlan? Can I do it as a default entry in the users file or is it needed somewhere else? Thank you very much, James