Okay, here's the deal. I need to make a script for my website, but I don't know how to! Can you help?

For a start, if you visit my website (www.girls-only.tk), you come to a page which asks you to choose a resolution and a flash/html navbar. How can I make a script that will automatically do that for you? Like, you go to the home page, and you click "Enter Girls Only" or something, and iMac users get an HTML bar, while Windows users get Flash, and the resolution fits the one of your computers. If you can't do that, maybe Netscape users get HTML and IE users get Flash ...?

If you could do that, I promise to put your banner on my website :)