You can upgrade to the Adobe Creative suite, but that will give you Photoshop CS, Illustrator CS, InDesign CS and GoLive CS. It will do nothing for AE or Premiere.
Assuming you don’t have a use for Ill, ID and GL you would be better off upgarding the individual products.
The only bundle with those products is the Video Collection Professional <http://www.adobe.com/products/dvcoll/main.html>. As well as Photoshop CS, After Effects Professional, and Premier Pro, it has Encore DVD and Audition.
No. All previous bundles had to be upgraded product by product. Previous to CS Creative Suite, upgrades to the products weren’t released simultaneously.
So you could use Photoshop 4 to upgarde to the Creative Suite (or just to Photoshop CS), but you would have to upgrade Premier and AE separately.