I have been playing minecraft for a while now and notaced it's quite laggy on my laptop, I am running windows 7 64x and I have tried 32x, I found that fo there to be no lag the settings had to be on normal or lower and fast set. I tried to use ubuntu but it failed :tongue.gif:, I came across Linux mint and tried it out, and I found that I was able to play minecraft full screen with fancy and far settings with no lag on any multiplayer server, I'm not trying to advertise Linux but I thought this could help out a couple of people who are playing minecraft on windows with lag, you should check it out, if you download "the standard version" it has java already installed on it so there were no issues trying to install it. You don't have to whipe out your windows when you install but rather install alongside windows.
If your having lag issues give this a try it worked wonders for me
Linux mint: http://www.linuxmint.com/
The os is only like 825 mb and is downloaded as an .iso so u need some sort of dvd burning tool or image mounting device.