When I did my program and extended into spring 10, I was able to sign up. Unfortunately that was before they started the registration for the classes online. :/
I'm extending as well and had the same question. I went to the education office earlier today (Suite 703 at Vista) and they set up a profile for me and gave me the link to the website so I could register. You can't sign up for classes until they activate your profile (it only takes a few minutes), so stop by the office whenever you get the chance and they'll figure it out for you.