To reiterate my previous post: If this is the speed you're getting when your modem connects, then the problem is with your phone lines or ISP, NOT your computer. Take out your splitter and see what happens if you plug the jack right into the wall.
Also, at some point, your phone lines enter the house. There is sometimes a jack in the wall there that connects your home wiring to the external phone lines. You can try plugging the modem in there. If it works better, you know the problem is in your house and it's not the ISP.
I used to work at an ISP. No matter how crappy the local DSL may be, it is ALWAYS better than a modem.