Hibernate was perhaps the most important option on my old laptop as it had a very bad battery. So if I need to take it off power, I had to Hibernate.
After I got my new Laptop with Vista, I currently use Sleep, but I still missed Hibernate during some situations. Obviously I tried searching the first couple of days, then gave up as I never could find the option that was supposed to allow me to enable Hibernate.
I was working on some stuff on my blog redesign when I found a blog entry by Deepesh(why don't you enable trackbacks on your blog, Deepesh) that had a solution.
Open a Command Window with Admin Access (My preferred way, type cmd in Start->Search, right click the shortcut, then choose Run as Administrator)
Type
powercfg /hibernate on
That's it, you now have Hibernate on your shutdown options.