DSL & NAT on W2K

I have a W2K server with 2 network interface cards, one connected to a
switch and the other one connected to a
DSL Modem bridge, the W2K is DHCP and DNS server

Im using NAT to share the internet with other computers in my LAN

The server surf perfect and faster the internet

Im experience some problems in the computers in my LAN
they cant open all the web pages, or they open too slow

The server open all the web pages ok, the problem is just on the computer in
my LAN

what Im doing wrong?