Creating DHCP Reservations across WAN

[Shaun11Turnbull]

I have four sites each running Win 2k3 Server DHCP. Each site has its own Scope, with either a 24bit or 19 bit subnet mask. All sites are on one Domain. I am implementing DHCP reservations at one site. When a laptop user visits another site I assume they will pick up a local DHCP address. I want to set up DHCP reservations at these other sites. The roaming users require a local IP address to access the internet and local resources, but also require access to the resources across the WAN. Currently, everyone uses DHCP and can view all local and WAN resources.
Is this possible? If so how?
Thanks

 

[Shaun11Turnbull]

Extra Info:
Site A: Mask 255.255.224.0
192.168.0.x - Servers/Printers/Routers/DHCP (Domain B)
192.168.10.x - Test Equipment (Domain B)
192.168.30.x - Server (Domain A)

Site B: Mask 255.255.255.0
192.168.96.x - Servers/Printers/Routers/DHCP (Domain A)

Site B: Mask 255.255.255.0
192.168.128.x - Servers/Printers/Routers/DHCP (Domain A)

Site D: Mask 255.255.224.0 (All Domain A)
192.168.160.x Servers/Printers/Routers
192.168.161.x - 192.168.189.x - Test Equipment
192.168.190.x - DHCP Reservations
192.168.191.x - DHCP

Planning for Site A & D to have VLANs for Test Equipment and Access control via Cisco ASA & ACS. Also migration of Site A to Domain A