How to expand existing DHCP

I am doing a complete refresh of all the PC's in my environment. I would like to create a subnet, or otherwise increase the number of usable addresses.

I currently have a 192.168.1.xxx network, with 2 sites, second site is 192.168.4.xxx. It is important that the new subnet allow easy communication to both sites.

Additionally I need to create a guest network, that allows subnet to has limited access to network resources but, does allow internet traffic.

I am kind of  a nub when it comes to this, so please dumb down any responses, and any/all direction will be appreciated.
RCroninAsked:
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vdh_techCommented:
Increasing your local subnet is no easy task.

I would start by finding your DHCP server.  Then changing the Subnet mask of both the LAN interface and the DHCP server to something like: 255.255.254.0 -- this would double the number of IP's you can use (192.168.0.1 - 192.168.1.254).  You would then need to find every device in you LAN which has a static IP address -- including the router/firewall, printers, phones, servers, etc -- and update them with the new 255.255.254.0 subnet mask.

The second site would not need to be touched except if it reference the 1st site's old subnet -- such as in a VPN tunnel -- then the subnet in the VPN tunnel would need to be updated.

Finally, the best idea for a guest network would be to setup a DMZ on your firewall.  The firewall would be able to create a special DHCP server for this new LAN -- you could make it's IP scheme completely different (172.20.1.X for instance) -- see here: http://en.wikipedia.org/wiki/Private_network.  The firewall would be able to separate this network from your internal LAN; however, you could add "access rules" to allow traffic between the two networks -- specific servers, ports, etc could be defined in the access rules.

For the resubnetting see here: http://en.wikipedia.org/wiki/Private_network

Since setting up a DMZ is different for every device, you need to lookup the topic from your firewall manufacture's user manual.
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vdh_techCommented:
err... For resubnetting see here: http://support.microsoft.com/kb/255999
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