CS2 is excellent and i really like the new Adobe Bridge.
Go to
www.adobe.com/products/photoshop/newfeatures.html to find out more.
But still CS2 is noth worth upgrading for a hefty price. Better stick to CS.
Also checkout
*www.google.com/search?q=Differences+between+CS+CS2&hl=en&lr=&scoring=d&start=0&sa=N
*forum.weborum.com/lofiversion/index.php/t2965.html
*whereisben.blogs.com/whereisben/2005/03/photoshop_cs2.html