I would configure your setup as such:
ISP > Speedstream 6300 > Linksys VPN router > 4 computers & server
1. The Speedstream 6300 is most likely a router & modem all-in-one (hence the 4 LAN ports). What you need to do is tell the Speedstream to NOT act as a router; therefore you need to go into the router's configuration utility and set it to "bridged" mode so that it does not use NAT (Network Address Translation) to firewall your network at that point. You want the Linksys to act as the firewall instead of the Speedstream, which basically means you have to tell the Speedstream to just pass the static IP onto the Linksys instead. Usually a call to your ISP can put you in touch with a support person that can walk you through setting up "bridged" mode in case you have trouble configuring the Speedstream on your own.
2. Disable DHCP on both the Speedstream & Linksys. This is something you want to install and configure on the server, along with DNS.
3. Log into the Linksys and setup the WAN port to receive it's IP from DHCP. This is not the DHCP service you will be using on your LAN, but rather you're just telling the router to go out and check for a DHCP server from your ISP which in turn will typically hand off your static public IP address to the Linksys. When this is complete and the WAN port receives your static IP, it should be displayed on the setup page of your Linksys WAN connection and you are now ready to focus your attention more towards the server in order to finish getting the LAN setup.
4. Install and configure DHCP & DNS on your server. For some tips check out YeOldeStonecat's server network guide:
Any other questions at this point, just post away.