802.1x dinamic vlan, using AD information

Hi all, I have a question. I use this combination: cisco 2950 sw as NAS freeRadius 2.1.1 as authenticator, Active Directory as the database, and the win xp client. It wokrs fine. I want one more thing, witch is dynamic vlan assignment. How can I implement it? My idea is enlarge the AD schema with vlanids and get it with freeradius and send to the switch. Is it good? or have an easier better way. I think somebody has met this problem, please tell me the solutions. Thank you. Gabor