Hello, actually photoshop cs5 uses less ram then cs3 ... i suggest you go with version 6 or 7.
anyway with cs5 :
-turn off opengl,
-set up a secondary cache partion (settings: ctrl-k , than search for performance) ,
- set the history to 5 steps (use unrobustive editing) ,
- and you can clean up your rams with settings / purge / all
hope this helps
and if you manage to make 5-6 websites with dreamweaver you will learn css and html