I don't think there is a difference but I think there is something about not being able to use it to sell work. Don't quote me on any of that though. Someone should be able to help and try google it can work wonders.
TJ
This is not true in the U.S. although I think it may apply to international editions. There is no restriction on using it for profit. The U.S. version of CS4 extended student is the same as the regular version. There is no license limitation after you graduate (specifically addressed in their FAQ).
Try again. You're strictly forbidden from using Student editions for commercial gain. Here is the entire information list from Adobe's Education Storefront (the way you buy their student editions):
Adobe Photoshop CS4 Extended - Student Edition
Get all the features in Adobe® Photoshop® CS4 software — and much more. Whether you work in design, motion graphics, architecture, education, engineering, medicine, or scientific research, Photoshop CS4 Extended - Student Edition is the software for you. Paint directly on 3D models and access all the power of Photoshop for 3D editing and compositing. Experiment freely with nondestructive image adjustments. Composite images, text, and graphics. Work at peak efficiency in a streamlined and flexible interface. Edit motion graphics over multiple frames of imported video layers. And for accurate image analysis and visualization, take advantage of precise measurement, counting, and logging tools.
Eligibility for Student Editions
Only full- or part-time students enrolled at a higher education establishment, defined as an accredited public or private university or college that grants degrees requiring not less than the equivalent of two (2) years of full-time study, or students enrolled at an accredited public or private secondary school providing full-time instruction are eligible to purchase Adobe Student Edition software.
Restrictions on use of Student Editions
You may purchase only one license of any Adobe Student Edition product. This license may be used only on your privately owned computer.
Student Edition products may not be used for commercial gain.
Submission of Academic ID
All purchasers on Adobe's education store will be required to submit proof of academic eligibility prior to shipment of order.