Yes, something has changed. The site we used (summer 2010) was here: http://epgy.stanford.edu/openenroll/signup.html

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Access to EPGY courses is no longer available through this portal.

To enroll in EPGY courses, please register your student at http://epgy.stanford.edu/school/openenroll/signup.

Bummer. I suspect they found that tech support made it uneconomical. There was some stuff (specifically, the geometry items) we never could make work. Schools have to provide a buffer person to handle that kind of thing.