Not possible with IE.
There's a CSS property for max-width and min-width, along with height too... but IE doesn't recognise these properties unfortunately.
You can cheat a little, make it dynamic for one browser and not for another, using the underscore "hack".
[code]
div#content {
min-width: 800px;
max-width: 1200px;
_width: 1200px; /* for InternetExploder */
}
The underscore hack basically works because IE doesn't recognise properties or names that begin with an underscore. Essentially, it ignores the existance of the beginning underscore, so whilst other browsers see _width and understand that there's no such property called _width, IE only sees 'width'.
Also, are you really working on this site? Because firstly, that doesn't look like a template that's just been designed and you're not sure whether to use it. That's a complete website, which apparently is finished and has complete content (and furthermore is currenty already live).