[B]I have made a website using a picture as background, and the resolution i worked in was 800 * 600… Now i want my pages to be automatically adjusted or stretched as per the screen resolution…
Also i am making another website, so plz tell me the best way to make it optimized for all browsers and resolutions[/B]
Please supply your URL so that we can look at your code and advise accordingly.
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I have not hosted it yet, isnt there a general way to do this
Have the image in a IMG element (within the HTML), use absolute positioning to tie it to the top & left hand side, set width and height as 100% and use z-index to ensure all other content and elements are placed over the top (rather than under it). It’s the cleanest way and it’ll give you the scaling effect you want. 
See this link for an example: http://www.ringvemedia.com/