Hybrid Dual WAN setup question.

OK, I have a question about how to set up dual wans to route p2p traffic to my non-throttled adsl account and move all other traffic to my cable modem. Both connections are wireless at heart, but the adsl in connected to my computer at the onboard nic via a wrt54g w/ ddwrt grabbing the signal and rebroadcasting via a VLAN to my nic. The cable can be connected via my wifi N pcie card.

What I would like to achieve, as stated above, is to be able to connect to both networks and subsequently both isps and route the different traffic to both, either automatically, or manually.

I have quite a few old boxes, nics, and routers laying around that could be used to build a linux/bsd solution if necessary.

I know I could just set up one of the old boxes as a freenas or the like, connect it solely to the dsl, and use it for managing my torrents, but I would really love a solution for my main box if not for convenience, also to feed this curiosity monster of a brain of mine.

Any suggestions? Thanks ahead of time!