Okay. I have an answer. Netopia's 6161 router can aggregate xDSL lines providing that the ISp you are connecting to supports multilink PPP. Pretty cool huh? You could effectively have 768/3.0Mbps from 2 ADSL lines for 100.00 per month. Blow me away. Better than a T-1 down and most of it up for 1/10th the price.
As for integrating the two network I still haven't got an answer yet. Anyone have any ideas how it's going to behave? My current theory is that since they are routers that they are going to only try to assign DHCP addresses to those clients directly behind them, and that providing I have each router assigning a different series of IPs there shouldn't be a problem.
One of you network freaks has to have tried this. Drop me an email if you have.