I just upgraded to Vista Ultimate. PhpED is running just fine so far, except for one small problem: window resizing is not working properly. When I resize the phped window, the editor pane does not resize to match. When I maximize the window and double-click the tab, all the toolbars, etc disappear but the editor pane remains the same size. Here's a screenshot:
http://neptunewebworks.com/tmp/phped_noresize.png

As i did this, I found that if I switch tabs after the failed resize, the editor pane does then resize correctly. So it's a pretty minor issue, but obviously incorrect interface behavior.

Please make sure you have all the latest updates/fixes available in Windows Update installed.
We observed the same problems with some early versions of XP too.