The monitor is rated at 5ms, so the lag you're seeing is likely not a monitor issue, but perhaps a video card issue. I would recommend checking to see if your video card has a driver update.
I own an alienware M15X laptop and today bought a Samsung T260HD monitor for playing games.
With a Corei7 @ 1.6GHz, 8Gb Ram and Nvidia 260M, I thought it should run Left 4 Dead 2 slowly (I can run on my laptop at 1920X1200 res)...
But not working on the monitor and I suffer from very bad video lag.
Why is this so? It makes the game unplayable... Tried installing the new driver but doesnt help at all.