Windows sizes

I been playing around with many windows sizes in flash. In the experience of those of you creating all flash sites, what is the ideal sizes to properly show content in a 800x600 and 1024x768?

What are some techniques and any other suggestions on dealing with creating initail windows sizes for certain resolutions?

I have seen people create start up dialog windows asking to choose a size then creating a cookie so tht everytime the visitor comes to the site they pop right into their correct size, can any one send me in the direction of achieving this?

Thanks in advance,