I still have to believe that the DHCP Server is not functioning correctly.
First it sounds like your default gateway is set wrong as pointed out above. Your default gateway should be the same as your router. You can set this in DHCP as I detailed above.
On your DHCP Scope (Server Options) did you set the correct values for:
003 Router - your router IP
006 DNS Servers - your DNS server IP (should be same as domain server)
015 DNS Domain Name - (Obvious)
044 WINS NBS Servers -Your WINS Server IP (same as domain server)
046 WINS NBT Node Type - should be hybryd (0x8)
Actually, I was trained to put the 003 router under the scope options and the remaining three under the server options.
To go back to what you mentioned about WINS, if you're running all Win 2000 clients and servers or XP, then no you don't need WINS, however, if you are running 98 or NT clients you do.
The DHCP server is what provides their DNS server IP, the IP number the default gateway and the WINS server information when you have the clients set to automatically obtain an IP. I can tell from the way that you've stated yourself and your experience with 2000 server that this is what you want.
I truly feel you need to look closely at all your settings on your DHCP server.
These are some key steps I was trained to look for:
1)To verify and confirm that DNS is working properly you should always, before installing Active Directory, ping your Server (localhost) and make sure you have a successful ping and then run nslookup at the command prompt. If DNS is functioning properly then nslookup should return the name of the default server and the IP address. If it's not, you have a problem. I the server doesn't appear in DNS immediately you can force reigistration by typing ipconfig/registerdns at the command prompt.
***Critical!!! - in order to use Active Directory, you need to enable dynamic updates in both the forward and reverse lookup zones!!! This May Be Your Problem***
You should enable scavenging.
2)Make sure you create a forward and revers lookup zone for your router/s as at least one of these will typically be your default gateway.
Key thing is for every forward lookup zone there needs to be a reverse lookup zone.
3)After installing Active Directory you need to confirm that in your DNS server that in addition to your original forward lookup zones you also have the additional following directories: _msdcs, _sites,_tcp, and _upd
If you do not, you have a problem
4.When setting up DHCP, you need to set up any reserved IP's (server, routers, etc), and set up the scope options and server options I detailed in my earlier post.
5.There's nothing you really need to do with WINS after installing except make sure it's running. (Remember as I stated earlier if you have legacy clients on the network you need WINS.)
That's a nutshell version of about 3 weeks of instruction. Hope it helps you resolve the problem.
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Just had an additional thought
Make sure you have DHCP turned off in your router - (many newer routers have a DHCP server built in and by default it's usually on. ) You can't have two DHCP servers running on the same LAN. The client machines will get their IP info from the first DHCP server that they communicate with, and they may just be picking it up from the router.