Regardless if you set up fog as your DHCP, or supply your DHCP server ip address, you still [B]NEED[/B] to supply the information of the next-server (your fog server) to your management console (DHCP server console) and reboot the network so that i can find the “next-server”. You also have to enter the file name that will be loaded on pxe boot.

[code]
3. Set up DHCP (For Windows DHCP)
[]Log onto your Windows DHCP server
[]Open DHCP console.
[]Right Click Scope Options -> Configure Options
[]Scroll Down to number 66 check and give the IP of FOGSERVER
[]Scroll down to number 67 check and give the value pxelinux.0
[]Apply and close.[/code]

Supplying options 66 and 67 are not OPTIONAL, they are REQUIRED.
This information came from a walkthrough on the forums, however there are MANY guides to follow to get FOG set up. There is even a different walkthrough on the wiki if you would like to take a look at that.
[url]http://fogproject.org/forum/threads/how-to-install-fog-on-ubuntu.5/[/url]