the modem can only physically do 53.3kbps (i think, i'm to lazy to look it up, but its somewere are there) max, there is no way to get faster with just a single modem. You can do modem bonding to get double the speed, but most ISP's don't support that.
There is no program out there that will increase your download speeds. propel is the only thing that can speed up browsing.