Establishing multisites on subdomains

Hi,

I have some difficulties creating subdomain sites. Can someone tell me what I’m doing wrong?

The main domain is http://osi.no. It’s the main site for a student atlete club with 25-30 different sports.
I converted the main site to WP some time ago, and want to allow all of our different groups to run under the main site, i.e. “soccer.osi.no”, “basketball.osi.no” and so on.
I went into cPanel and created subdomains for all of the different groups, and originally thought about creating separate installations of WP for each group. However, the current hosting plan only give us 4 mySQL servers. Thus, I thought about using multisite.
I’ve installed MS, using the following wp-config and .htaccess

define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', true);
define('DOMAIN_CURRENT_SITE', 'osi.no');
define('PATH_CURRENT_SITE', '/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]
RewriteRule . index.php [L]

When going to Network Admin -> Sites -> Add new and attempt to create, say “xyz.osi.no”, I either 1) get a HTTP 500 Internal error, or 2) I get a page saying that page was created, but when accessing the site there’s nothing there.
Any ideas?