Webpage Alignment

Question

Hey friends... I'm developing a website using ASP.NET in Visual Studio 2008. I use C# as the programing language. My problem is....the alignments of the website are always change.I use tables.And the other thing is if I try to open this website under various resolution(widescreen, 15" or 17" monitors)it changes all the alignment. like header goes somewhere or some rows of table go somewhere. Now my website in a bad position and I want someones help to overcome from this problem since this is my college project. Thank you !hope somebody give me an answer as quick as possible. Charith