To enable pretty permalinks, or ‘clean URLs’ as it were in drupal speak, WP needs to be able to write to .htaccess. The file should live next index.php on the folder specified as the URL on Genereal > options. If it does not exist, upload 1.htaccess.txt and rename to .htaccess.
This is the code that needs to go in it
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress