After starting Silverstripe the first time I get the configuration page (install.php).
When I submit this page after a few seconds I see the following message:
Checking that friendly URLs work...
Friendly URLs are not working. This is most likely because mod_rewrite isn't configuredcorrectly on your site. Please check the following things in your Apache configuration; you may need to get your web host or server administrator to do this for you:
mod_rewrite is enabled
AllowOverride All is set for your directory
Extra info: installed on Windows 2003 Server / IIS 6 / PHP / FastCGI / ISAPIRewrite (free version)
The only thing I can think of is that your rewrite module isn't working properly.
There's a part in the installer that does an AJAX request to InstallerTest/testrewrite which is generic for any rewriting capability - so this means it'll work for the IIS 7 rewrite module, Apache mod_rewrite or ISAPIRewrite if it's setup correctly.
I'm not too familiar with ISAPIRewrite and installing SS on IIS 6, as I've only installed and used SS on IIS 7 and IIS 7.5.
I assume ISAPIRewrite uses some form of .htaccess file for configuration?