Macbook Pro and external monitor problem

Hello everyone. I have an issue with my 2010 Macbook Pro when connected via hdmi cable to my 28" monitor.

I try and set it to 1080i, it works but the screen flickers. I've tried setting it to 1080p but the picture is grainy. The next resolution 720p works, but everything looks bigger.

Has anyone else had similar issues? I'm thinking that it might be better if I use dvi rather than hdmi?

 

This is the monitor

http://pless.co.uk/product.php?productid=9416;

Just don't understand why it would flicker at the 1080i setting. A lot of the other resolutions produce a grainy screen.