I have setup a subnet between the routers, and assigned one of the DMZ IPs to the primary interface on the router:
Interface vlan z
ip address x.x.x.y 255.255.255.0
You will need to configure routing, again whether that's a dynamic protocol such as RIP, EIGRP or OSPF, or whether you just use static routes, is up to you. If the DMZ network is a single subnet, or can be summarized, I'd just do a static route on the existing router pointing to the new router as the next-hop to get to that subnet. This command is for a /24 subnet:
ip route x.x.x.x 255.255.255.0 <DMZ router interface>
The new router will need default route pointing to the existing router as the next hop to get out.
ip route 0.0.0.0 0.0.0.0 <existing router interface>
Ive done all this and it all seems to work, the problem is the second I enable NAT on the second router, all the IPs I ping through the primary get translated to the interface on the primary router, which is causing me problem. I also have a port for its vlan 1 plugged into a switch but the switch doesnt seem to be picking up the vlan on the second router. Any help would be awesome