Load balancing downloads

ok, so my problem might be a little complicated.

as of right now, my network is set up like this


ISP................... ISP
|.......................|
Router............. Router
|.......................|
-------AP--------
......... |
computer-computer

now how I have it as if one network is clogged the browser will auto switch to the second ISP, but im looking for it to load balance between the two so instead of 5mb/second it will switch to 10mb

Way back when, there was a way to do this with dial-up modems.

I have no idea how to do it with two separate ISP's.