Download a demo of each and try.
Premiere Elements 4 bears little resemblance to Pro in workflow and features. It is really SIMPLE…tooo simple for you. It has none of its own magic features like Photoshop Elements. Very little one learns from Premiere Elements can be applied to Pro, unlike Photoshop Elements.
While Photoshop Elements is a cut down version of Photoshop, it is still quite powerful. It has many undocumented features of the full version kinda hidden, like holding the Alt key down while adjusting levels to see what is being crushed. Most of what one learns in the Full Edit mode can be applied to the full version of Photoshop.
I teach both on occasion at a local Career Tech school. I run out of things to teach in PE after about 8-10 hours, but PSE class runs 24 hours and leaves students overwhelmed and awed at the possibilities.
Premiere Elements 4 is quite similar to Movie Maker in worlflow.
Photoshop Elements 6 is quite similar to Photoshop plus a lot of extras.