Bridged Router

I have setup a Westell 7500 in bridge mode, I also turned off DHCP in the private LAN settings.
My G5 Tower (Sever 10.5) only has one built in Ethernet card and I know this is a little unorthodox, but I set NAT to use the Airport to connect to the router via the static IP Verizon provided. I set the built in Ethernet to serve the local network to give about 10 users access to file sharing and the internet. We do host two small web sites on our server, but the traffic is minimal. Our mail server is being hosted off site. Everything works good with the exception of upload speeds, especially email. We are signed up for 3 Mbps / 768 Kbps. We are only getting about 150Kbps if that. Verizon says the line tests are fine. Any suggestions would be helpful, thanks in advance.

More Info.

I called Verizon to test the line and they found issues, of course they made me set the router up without my server to test my end and they did improve the upload speed. The set the router back to the settings I was using for the server and got the same improvement. There does seem to be some degradation when there is a lot of activity on the server, IE Time Machine or several users sending at the same time.

I would like some input on something I described in the first post. Since my G5 tower only has one Ethernet port, I setup the Airport to connect to the Verizon Router with the static ip they provided. I have set NAT in the Mac Server to forward to the Ethernet port from the Airport and DHCP to give my local users IP addresses. Is this OK or should I just let the router handle the NAT?

Thanks for your help