I have installed Drupal 7 on a local computer on stack called Denwer (similar to WAMP) and Windows 7; I see that all pages load without Overlay module (it is on, on modules page). I guess that jQuery does not work at all: Views slideshow doesn't work, when I add node all parameters load in a list instead of paging-listing mode.
I cleared all caches, reinstalled Drupal 7 using the development snapshot, clean-installed Denwer: all this doesn't work.
I remember I didn't have such problems on Windows XP.