In doing a new installation of 2.0.5, on a host called http://www.webxtra.nl, when browsing to the
wp-admin/install.php script, the browser prompts to download the file rather than execute it.
After trying several things including putting "DirectoryIndex index.html
index.htm index.php" in the .htaccess file and asking the host to check the
webserver configuration, found the host was not providing enough resources
The solution was to put the following line in .htaccess:
php_value memory_limit 16M
Hope this helps someone else.