Ok, here's the situation:

I've got both cable and DSL at home. I usually surf by cable, but since it's not entirely stable and reliable, I have the DSL connection in case it's down. Both cable and DSL are connected to my PC via ethernet.

Now, if the cable connection goes down, I simply disable (in software) the ethernet card through which the cable modem is connected, I turn on my DSL modem, dial in and voila: instant DSL connection.

But here's my question:
Now and then, the occasion arises where I could use both connections at once. Eg. I use bittorrent to download two huge files. I usually use the DSL for that because I've noticed it works better for these kinds of applications. This means the cable's ethernet card is disabled.

If I want to do any regular surfing now while I'm using Bittorrent, things are SLOOOOW. Now, my idea was, to enable the cable modem's ethernet card as well and surf via the cable modem. Unfortunately, this doesn't work because my browser obviously also tries to use the (already clogged) DSL pipe.

So, what I would really need is a program with which I could point out which application should use which ethernet card. Eg. Bittorrent ethernet card #1, Firefox ethernet card #2, and which would keep both connections competely separeted from each other.

Does such an application exist?

Thanks!