two adsl line

i want to lend 2 china-telcom adsl lines,each line is 2M,
how to make it work just like one 4M line.
whether it can work?
because there are 2 gateway ,i don’t know what to do.
thanks

I use

http://wiki.mikrotik.com/wiki/Routing

And am gratefull to the author.

It will not download at 4mbps on 1 file but will on mulitiple files