I can't add a URL to the dock

The divider in the Dock is a thin vertical line separating Applications from Files/Folders. Your weblocation must be to the right of the divider as it's a file - try placing it to the immediate left of the Trash. As to the whatever-it-was you added, if you can add an ordinary file to the Dock you should be able to add a weblocation just the same. Try with a TextEdit file or something and see what happens.

I think I see - are you trying to drag the actual URL as displayed in the top bar of the browser? what you need to drag is the little icon to the left of the URL. If you drag this to the Desktop you get a file which when double-clicked will open the page in your default browser, and you can also drag it to the Dock as you have been trying to do.

Check out this site for changing icons
http://interfacelift.com/icons-mac/faq.php#4

Thanks - yes, not being able to mark an item helpful or solved is an annoying bug on these boards which has been reported many times.
The important thing is that your problem is solved.