SWF won't play in web browser

Using Flash CS3 and ActionScript 3.0, I put together an interactive version of my company’s print catalog. I’m new to programming and it took me a really long time to get the thing working, but, at long last (and thanks to some input from this forum), I finally got it. Now, my problem is that the SWF will not play properly in a web browser. It works fine in my stand-alone flash player but when I insert the SWF into an html file the actionscript goes completely haywire; my urlrequest and imageLoader fail to work and my navigational index behaves in bizarre fashion. Could this be because my stand-alone player is version 9 and my browser plugin is Flash Player 10? Is there something I’m missing in the settings perhaps? Please lend my some advice. I’ve got a lot of time in this project and it’s all for naught if I can’t get it online.
Thanks!