Did you purchase a download option from Adobe directly or did you make the purchase through your school? If it was not purchased with the option to download from Adobe directly then it would be expected for you to not have access to the install files.
Often schools and educational organizations refer their customers to download our trials instead of hosting the install files themselves.
You can find links to older versions of our software on the Prodesigntools.com site. You can find more details at http://forums.adobe.com/thread/981369.