Let's say I have a site:

Example Web Page

Which technically is Example Web Page

Currently Google gives the following:

example.com/ - PR6
example.com/index.html- PR0

1) Why is this?
2) Does that mean that Google takes whatever "index page" is served by the webserver and attaches the PR to the domain.
3) Does this mean I can switch just the index page to say 'index.php' and not have any PR problems with Google?

Thanks!

-K

Google gives PR to URL's, not pages..

2) Does that mean that Google takes whatever "index page" is served by the webserver and attaches the PR to the domain.

No, They give PR to every URL that has links to it, Regardless if some of those URL's are serving the same page..

3) Does this mean I can switch just the index page to say 'index.php' and not have any PR problems with Google?

Your PR that is visible from domain.com won't change, But the PR for domain.com/index.php will initially be 0 untill you get links to it.

An object lesson in why you should never link using the name of the default document.

So in Google eyes, the following are different URL's even though they are the same physical file on the server

example.com/
example.com/index.html

So if I don't link to the index.html (which I don't), either internally or externally, then I really shouldn't be worried about switching the index.html to say index.php. I should probably still do a 301 just in case someone else has linked to it. But as far as PR goes, I shouldn't be effected by this.

-K

What's PR got to do with anything (the imaginary number you can see anyway)

correct if you never link to the index page filename, there will not be a problem.

Be careful with redirecting from index page to the root folder. Unless you set it for the specific condition of the requested URI NOT the served URI you can cause a redirect loop to occur.