I have to use a flexible or centered page design that works even for users screen resolutions of 800*600. When I make my page smaller, the elements are moving and changing their
The best method to control what is going on with your page when trying to limit size restrictions is to assign different stylesheets to change the site subject to resolution. These will be for users that are accessing your site using different resolutions.
http://css-tricks.com/resolution-specific-stylesheets/: link provided
This issue has troubled many designers for a long time and back in the 90s when fluid layouts were all the rage this problem had to be overcome.
Bare in mind that with the development and growing usage of mobile devices to view webpages, making a mobile version of your site then this is also the method to take.
In doing this you are applying a totally new layout of your webpages to make best use of the available space. Also, if a users browser does not support this declaration then they will still be able to view your site.... Everyone is a winner.