simple questions, but the answers have eluded me.

1. Is the file supposed to be named googlesitemap.php.txt, or is it supposed to be named googlesitemap.php ?

2. At Google Webmaster Tools >> Site Configuration >> Sitemaps, do I want to enter the URL as /googlesitemap.php... or do I want to enter the URL as /sitemapindex.xml ?

3. Does the file /googlesitemap.php create a brand new fresh /sitemapindex.xml file "on the fly" when google crawls it? Is that why we are supposed to use /googlesitemap.php at Google Webmaster Tools?

4. I installed the mod correctly, but at Google Webmaster Tools >> Site Configuration >> Sitemaps, when I enter the URL as /sitemapindex.xml, the Sitemap area of Webmaster Tools says that the URL /sitemapindex.xml has an "error" (red X), but when I click on it to see more information about the error, it says "no errors found." What the heck is that about?

thanks..
Jim