this has been asked and someone did post the site. But its complicated as you will have two different ip address from both providers and some how combine them to work together.
There are some far more expensive ones out there, but I'm interested in this one myself. Nexland had a good one, but Symantec acquired them and I can find nothing on their website about it.
In Windows (XP, maybe 2000 as well) if you have two nics and they are each connected to a modem, then you can either multilink or else bridge the connections. I think the former is the correct choice. Should be in network properties once all of the equipment is installed.