Due to a limitation in Cisco / Windows integration there isn't a ready way (assuming the use of secure update zones in your DNS server) to have this function directly from the Cisco side.
The Windows DNS server expects Kerberos integration to validate the credentials. The Cisco kit doesn't do this.
Turning on the insecure update option on your reverse lookup zones in conjunction with the update both setting on the Cisco DHCP server will get this to function, albeit at a reduced security level.
The best option is to have the Windows devices perform their own registration. This behavior changed between XP and Vista so that this doesn't occur by default.
To configure this behavior a group policy with the following settings will do it.
Computer Configuration \ Policies \ Network \ DNS Client
Connection Speciffic DNS Suffix: example.com
Dynamic Update: enabled
Register DNS records with connection specific DNS suffix: enabled
Register PTR Records: Register
Depending on OU structure this can be filtered to only workstations running Vista or higher as needed.