|The three have to be physically connected for route tables to work and the routers lan ports would have to support routing which most soho routers don't.|
buy a real router that supports 3 adsl wan ports that also supports vlans on the lan side.
put a router between net1 and net2
put a router between net2 and net3
If you are a glutton for punishment extend this from 2 to 3 networks