incrediBILL - 2:46 pm on Jul 19, 2010 (gmt 0)
It's like a PR Bomb went off on our site, wiping some pages to 0 and others to 5.
Well not exactly.
You changed the file names and the new file names aren't in Google's visible PR toolbar, you cannot determine anything from the toolbar alone at this point.
If the rankings only dropped from page 2 to page 3 you may want to just site tight and wait, possibly tweaking any text to make sure your ranking keywords are more prominent.
Here's a simple experiment, replace a handful of your old pages that ranked well back where they used to be and see if they return to their normal place in the search engine in a week.