[support] Modify template of node/add/something?

Hi, I want to use a bookmarklet that opens a window in node/add/bookmark with the url of the page where I clicked the bookmarklet in a url field I've created with cck. So the bookmarklet opens something like this: http://example.net/node/add/bookmarket?url=http%3A//www.google.com/ Now I want to know if there's a way to modify the template of the node add page so I can populate the url field with that variable. Is it possible? -- If you're not making art with the intention of having it copied, you're not really making art for the 21th century.