Resources from Adobe.com for Photoshop
Straight from the Horses mouth - So to speak!
:-)

Photoshop CS3 Help Manual
PDF http://help.adobe.com/en_US/Photoshop/10.0/photoshop_cs3_help.pdf

Compare Photoshop CS4 Versions
http://w1000.mv.us.adobe.com/mena/products/photoshop/index.html

Compare Photoshop CS4 Versions
http://www.adobe.com/products/photoshop/compare/

Adobe Design center - THINK TANK AND DIALOG Center
http://www.adobe.com/designcenter/

Photoshop Help and Support
http://www.adobe.com/support/photoshop/

Photoshop CS4 Help from UK Site
http://alist.adobe.co.uk/products/photoshop/photoshopextended/

K-12 Instructional Support Docs Lesson Plans and more
http://www.adobe.com/education/resources/k12/instructional/

K-12 Online Community and documents
http://www.adobe.com/education/community/k12/

Adobe Education Home
http://www.adobe.com/mena/education/

Adobe Digital Schools Collection by Curricular area
http://www.adobe.com/education/instruction/adsc/