If your DHCP server is also a domain controller, then you are probably fine, if not, then you may want to see if the DHCP server is a member of the "Dns Update Proxy" group in AD.
Make sure the reverse zone is AD-Integrated and also check the Zone Transfers tab and make sure they are allowed (generally Only to servers listed on the Name Servers tab).
Also make sure your DNS server are listed on the Name Servers tab. Ok so given that your DHCP server is not registering the records on behalf of the clients, and aside from your windows clients not being set to register with DNS on their NICs (which you should verify in TCP/IP properties on the client NIC), I would check the security settings on your reverse zone to make sure clients are allowed to register in the reverse zone.
This article covers the default security settings for DNS zones: the settings are jacked up (or even if they are fine), you might try just blowing away the reverse zone and recreating it since you basically have a non-functioning reverse zone as it is...
The forward DNS entries ("A" records) for windows machines on the domain are populated automatically.
However, the reverse DNS entries ("PTR" Records) are not.
The reverse lookup zone exists, and I can add entries to it manually, but it doesn't automatically populate.Dynamic updates are enabled for both the forward and reverse zones. This could be due to a couple of different things: 1) Are your clients obtaining IPs via a Windows DHCP Server?If so, your DHCP server may not be configured to auto-register their IP with the DNS server.To check, right-click your DHCP scope and go to properties.On the DNS tab enable DNS dynamic updates and set to "Always dynamically update..." Also enable Dynamic Update for clients that do not request updates.1a) Even if these are enabled, you might need to make sure the DHCP server has permissions to update DNS records.