That depends on your target audience. If you want the largest audience, go for 640 X 480.

If the application is aimed at a single client and you know that all the users use a screen resolution of 800 X 600 or higher or if you make it a requirement to use your application, use 800 X 600.

If you have the time or you want to get the best of both world, make your form resize themself depending on the current screen resolution that the client is using.

My 0.02$

>Is there a standard for the size of forms in a system. Is 800 X 600 the standard or 640 X 480? Or does this depend on user needs.