Port 53 is for DNS.
The DHCP port is 68 (UDP).
I'm not sure of the IP of the DHCP server (Can't remember it, & I can't find it as I connect using a Linksys router).
Have a look at these two pages on Robin Walker's CM Tips site, for info on DHCP, firewalls, & more:
DHCP Issues
Firewall Config
EDIT: Looking at Robin Walker's site, you may need to add more than just the DHCP server's IP to your firewall's "trusted zone". DNS IP, UBR IP....Lots of info there, & settings for different firewalls.