i have no idea why you're getting access denied with your domain admin account? is the client pc a memeber of the domain?
and dhcp from where? you have dhcp running on your server or is it your router dishing out ip addresses? if it's your router, disable that and setup dhcp on the server. i'd imagine your setup being something like this....
router
ip 192.168.1.100 (dhcp disabled)
server (you must set the following properties manually in the network card properties)
ip - 192.168.1.101
preferred dns server - 192.168.1.101(this absolutely must point towards itself)
subnet mask 255.255.255.0
default gateway 192.168.1.100 (must point towards the routers ip address)
in the dhcp management console you'll need to setup a scope with the range between, for example, 192.168.1.103 and 192.168.1.120. then you'll need to activate the scope. also the dhcp server needs authorising within active directory. just right click the server in dhcp console to carry out these tasks.
finally you'll need to set the scope options in your dhcp console.
router (option 3 i think) - router's ip address (192.168.1.100 in this example)
dns server (option 6 iirc) - server ip address (192.168.1.101)
now your client pcs should pick up these settings automatically and use your server and router for active directory and internet access in perfect harmony...