Getting cookies

I'm having a problem with my script MySpace Birthdays on Homepage. While you're on your user homepage, there's a GM_xmlhttpRequest that grabs the listing of your friends who have upcoming birthdays, and the script places that information on the homepage. I've found that the xhr now returns a login form unless the MYUSERINFO cookie is part of the request.

The browser sends the MYUSERINFO cookie whenever it requests a MySpace page, but I can't access it via document.cookie. (If I could, this would be a trivial problem to solve; I could just grab MYUSERINFO out of document.cookie without having to store it anywhere.) The only other way I can think of getting the cookie is to try to catch it while it's being set (at login), but I can't seem to do that either.

I do realize that this might be impossible because it's a security risk, but getting the user's MYUSERINFO cookie and allowing the script to work automatically would be much more convenient than having people enter their cookie information manually.