how can i fix the size of my web pages for different type of screen?

how can i fix the size of my web pages for different type of screen?
the pages looks incrediblly different in another PC than in my PC

First of all, dont assume that anyone viewing your page can view wider than 800 px. While most people can, there are still alot of people out there who either have small monitors, or choose a lower resolution to be able to see better.

We need more information to answer this question adequately. Is it the size of the page that is the problem? Is it the way the html is being handled by different browsers? Is it javascript errors on a different system? Is it a descrepancy in the way different browsers handle transparencies in images?

Like LinuxChique said, assume everyone that views your site is viewing it in 800 x 600. Also, try using absolute values like 750px instead of relative values such as 100%. There tends to be less varyiance that way. There's also the scroll bars, they're usually about 15px wide. When I make a website I usually max the pages out at 750px just to allow a little wiggle room.

Hope that helps. Good luck!