oriecat,
What you are basically talking about here is called a fluid design. It means that your pages will stretch in both directions to fit a window size, or, conversely, shrink to fit a smaller window size, and still look good. In order to do this, the best way to approach it is to design it to look best in a smaller window, and then worry about how it looks in the larger window.
You might try looking at A List Apart for many articles and discussions on fluid designs. This is only one resource that is available.
My suggestion is that you start with a design that fits nicely into an 800×600 window size, and leave it at that. Once you have “perfected” it, that is, get it going and working exactly as you wish it to, then start to experiment with more dynamic layouts. The one thing about fluid layouts for newer web designers, is that it brings a lot of extra issues to consider. Let’s not even get into the fact that someone viewing your page may think the text is too small, and will manually re-size it. Then what happens?
I’d also visit Community MX for a whole slew of great articles all about web design, CSS, PHP and anything else you can think of. They have many free articles, and you can purchase individual articles for a small fee, or even subsribe to the site and have access to everything. They have an excellent support forum as well.
A bit of reading and research will help you define your goal for your site, and you can have a better idea of the kind of work involved to get it to where you want.
I hope this has helped you. Don’t forget to have fun! ??
Craig.