Installing Wordpress on Windows/IIS, error when accessing wp-admin/index.php

Hello, I am trying to add a Wordpress blog to an existing site.  I have the MySQL database set up and loaded, but when I tried to access wordpress/index.php, I got the error

Fatal error: require_once() [function.require]: Failed opening required './wp-blog-header.php'

I went into wordpress/index.php, and changed the reference from './wp-blog-header.php' to 'wp-blog-header.php', and that solved that problem.

But I get the same kind of error when I try to access wordpress/wp-admin/index.php

Fatal error: require_once() [function.require]: Failed opening required '../wp-load.php' (include_path='.;c:\PHP5') in D:\Inetpub\xxxx\wordpress\wp-admin\admin.php on line 20

I looked at the code for admin.php, and I the relative file reference looks OK to me.

if ( defined('ABSPATH') )
require_once(ABSPATH . 'wp-load.php');
else
require_once('../wp-load.php');

If I'm in wordpress/wp-admin/admin.php, I think that the reference of ../wp-load.php should point to wordpress/wp-load.php, which is a valid non-zero-byte file. Any ideas?

It feels like it might be a Windows vs. Linux thing, but I don't know enough to try different things out.

Thanks!