Screen Resolution Check

[susannem]

I need a script that I will check the users screen resolution and if its 800x600 or less then it needs to prompt them letting them know that they will not be able to view the site with their current screen resolution.

[Vladdy]

screen.width and screen.height will do that.
However, screen resolution has nothing to do with the width of browser window and designing sites so that one needs certain resolution to view them is a bad style.
What if someone who uses WebTV or PDA visits your site.
You should adapt you site to whatever user is using to access it, not the other way around.