I have not done this myself, but I don’t think it is anything difficult. For instance, with the archives, first you need to change the content class to be narrowcolumn, and add get_sidebar() before get_footer().
But if you are doing a fresh install, of course you will not run upgrade.php. Who would’ve thought that you still need to run upgrade.php even if u did a fresh install of WordPress 1.5?
I had the same problem. You must have a fresh install of WordPress 1.5, this is a bug in the final release. To solve the probelm, run wp-admin/upgrade.php.
@macmanx: Thanks for ur detailed reply, I tried that but it still doesn’t work. The download windows still pops up and offering me to download the WordPress’ index.php file.
@kafkaesqui: Thanks for the suggestion, it solved the problem. So I assume that it is a bug in this final release of WordPress v1.5.