New Network Layout Questions

UPDATE: COULD NOT EDIT ORG POST



ok, we are attempting to add/update some functionality to our network and servers, and i have a view questions that i hope some of you brilliant people can help me with:


currently we have an SBS2003 server setup with ~5 clients.
After disputing the upgrade method, we decided to purchase a new Server with SBS2008.

a couple of things we are looking at doing:
1. Create a Fail Over DC with the SBS2008 as Primary DC, use older server as Secondary DC.
2. Add Guest Wireless for clients. (reason this was posted here)



these are my thoughts/questions:
1. Can we run 2 copies of SBS on the same domain?
1a. if not, can SBS2008 be primary DC, and a copy of Server 2003 Standard be Secondary DC?

2. our budget is shallow, just barely enough to buy a decent server, so high-end networking is out the door.

currently our network topology as is follows:



what i am thinking about doing is this:




with the Guest WLAN AP acting as a router, and the SBS08 acting as a Router.
the Guest WAP would have a subnet: 192.168.100.0/24
and the SBS08 would have a subnet: 192.168.16.0/24



this way the SBS08 server would see all the traffic from the Guest Network as "Outside" or Internet Traffic, and we could protect our network from it with the firewall on the server.