> Now AFAIK, in *theory*, the bandwitch should combine, because the TCP/IP packets
> would journey through both connections, back and forth. But would residential
> lines allow for such things? Would the bandwitdh be really combined?
The matter is that under Windows, as far as I've seen, address ranges are "bound" to one network interface. For different address families the OS assigns routes to different interfaces, and you can see it by typing "route print" in a command prompt.
I really don't know what happens to the routing table when you have two working internet connections, could be that the last one overwrites the table, or maybe it just adds routes. At any rate you shouldn't have clashing rules: as soon as a rule matches, everything else is probably discarded.
What you CAN do is add your own routes to the table, so that you will use one connection for a set of addresses, and the other for the rest. Using both connection to reach the same target is probably possible, after all you'd appear as two different IPs to the other end of the cable, but not easily done on your side: I doubt Windows is able to manage multiple connections to the same internet aread to take advantage of them. Maybe Linux? But I can't help you there, ask Halcyon maybe.
Post your progresses, however.