Two things - you can either design a site to be best viewed at the lowest common denominator (these days 800x600 still persists), or you can treat the web as it was intended.
If you want to have absolute control over how the user views your work - use print, and stay away from the internet. If you want the site to look exactly the same on every computer, you'll go crazy.
Imagine this:
[rant]
A user looks at your site on a Window XP machine with the google toolbar, yahoo toolbar, ebay toolbar, and a few other toolbars installed, the MS Office shortcut bar is there, and a few other things which take up space, like the Start Menu, title bar, menu bar, address bar etc
Suddenly, you're reduced from having a 1280x1024 resolution to about 800x600 anyway.
Then along comes someone on a Mac using Safari with a totally different setup.
After that someone running Win98 with Netscape 4 joins the party, as does someone running Firefox on a Linux box.
Someone who's mindful of bandwidth rolls up, and has all images and stylesheets turned off, and then they're in a bit of a pickle.
Never mind the poor kid who's forced to use Lynx because he's only got DOS.
[/rant]
You have to allow for users to look at your stuff the way THEY want to, with just a little bit of guidance.
maulik started you off on the right idea - Use relative sizes for as much as you can, for example
Code:
<style><!--
table {width: 100%;}
h1 {font-size: 110%:}
-->
</style>
This way you give your users more freedom
I am a loud man with a very large hat. This means I am in charge