800x600 or 1024x768?

One method is to use Google Analytics.

Any decent web stats program should be able to tell you the screen resolution of your visitors.

If your hosting account doesn't offer that, you can use a free service such as statcounter.com

The "System Stats" link is what you will use once you signup and install their little code snippet on the pages you want to monitor.

Very simple answer if you think that your visitors are young rather than old then 1024X768 is best and if its vice versa then 800X600 should be there....

Got my point...or not ?

If you choose 1024x768 this will be bad for visitors which uses 800x600 if you choose 800x600 this will be not nice for visitors which uses from 1024x768 to 1400x1050, but big role playing your content, at my sites I can't set 800x600, but how sad roarmeow some people definitely still use 800x600 i can give you some example from 51,485 visits i have got 5.16% of 800x600 and 46.60% of 1024x768.

yeah, I work on 1680x1050 so all static websites look small in comparison to that ... and many of the stretched ones look empty ... I'd still make it for 1024x768 if it were me ... I just think 800x600 resolution is so old fashioned that very few people use it ...