Why not just go to the source.
http://kb.adobe.com/selfservice/viewContent.do?externalId=kb402371&sliceId=...
Turns out you can upgrade educational versions, just not at the educational price. IOW, buy educational version of CS3 then when CS4 comes out, you can upgrade to CS4 for the same price anyone that owns CS3.
Some software is missing some of the extras, but as far as I know AECS3 educational and full retail are the same in features and plug-ins.