I have two dedicated servers and no hardware firewall. I'd like to forward all requests that come into the primary server on port 1008 to be fulfilled by another dedicated server on the same network. I know I need to set up some kind of TCP proxy, but I first heard of IPTables yesterday. Any quick tips?
Carson is right: put a bridging firewall between servers and clients. Shorewall (IP tables) can then redirect traffic to different ports and different machines.
With the firewall being a bridge, you don't have to change your network settings, yet the bridge interface has to be assigned one IP address of each network clients and servers are in. Else the redirection won't work.
Caveat: the machine where the connection originally was pointed to has to be online (means: its IP address has to be in use), else the redirect won't work.
If the redirection is meant as a means of failover for high-availability, I would consider a load balancer (cluster) instead of the firewall, which leads to linux virtual server (for a general approach) or to a load balancer software like Apache (with mod proxy_balancer), balance or pount (if only http request are to be balanced). There's also hardware appliances like from f5 for load balancing.