Windows Server DHCP assignment based on MAC of client

I think this is what you're looking for.

"To configure a new filter

Open the DHCP snap-in.

In the console tree, double-click the applicable DHCP server, double-click IPv4, double-click Filters, and then right-click Allow or Deny.

Click New Filter, and then type a MAC Address and Description. Description is an optional field.

"

"The MAC address can either be the full address or a MAC address pattern (wild card). Following are the valid MAC address wild cards:

00-1C-23-*-*-*

00-1C-23-20-AF-*

00-1C-23-20-*-*

001C2320AF4E

001C*"

EDIT: Source http://technet.microsoft.com/en-us/library/dd759190.aspx

The proper way to do what you are asking would be use to Policy filtering at the scope level.

You can change what PXE Boot options if your DHCP is serving and several other DHCP options as well as IP range and denying service.