One opensource solution is to use ipmasqadm.  From the man page:

   EXAMPLES
       Redirect all web traffic to  internals  hostA  and  hostB,
       where  hostB will serve 2 times hostA connections. Forward
       rules already masq internal hosts to outside (typical).

              ipchains -I input -p tcp -y -d yours.com/32 80 -m 1
              ipmasqadm mfw -I -m 1 -r hostA 80 -p 10
              ipmasqadm mfw -I -m 1 -r hostB 80 -p 20

-Doug Winterburn

Date: Thu, 28 Sep 2000 11:23:24 -0700
From: Kevin Buettner <kev@primenet.com>
To: plug-discuss@lists.PLUG.phoenix.az.us
Subject: Re: Load balancing using a Linux Box?
Reply-To: plug-discuss@lists.PLUG.phoenix.az.us

On Sep 28, 10:02am, Justin wrote:

> Is it possible to do Load Balancing on my webservers using a Linux box?

Red Hat has an HA product that you may wish to look at.