Look on
http://forums.gentoo.org
If it can be done, I'm sure someone there knows. They have about the best repository of information I've come across.
Here is a direct link that addresses load balancing via iptables in linux:
http://www.ibiblio.org/pub/Linux/doc...ARTC.LOADSHARE
Nexland makes a dual WAN product with a dialup backup ... Xincom also makes one. It may be much easier to find a hardware router for aroudn $200 than try to set up a load balancing router via linux. I've taken a look at that article above (easily the best on the subject) and unless you are very linux savvy you will get lost quickly.