PS Benny in the .htaccess I have also tried subsite1.mysilverstripe, since I want to access the subsite via http://subsite1.mysilverstripe

# Subsite rewrite
RewriteCond %{REQUEST_URI} !(\.gif)|(\.jpg)|(\.png)|(\.css)|(\.js)|(\.php)$
RewriteCond %{REQUEST_URI} ^(.*)$
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{HTTP_HOST} ^subsite1.mysilverstripe$
RewriteRule .* sapphire/main.php?url=%{REQUEST_URI}&SubsiteID=1&%{QUERY_STRING} [L]

and Benny i presume your vhost.conf is the equivalent (the file I should be trying to replicate on my WAMP machine) of my WAMP httpd-vhosts.conf files??? I'm not 100% sure.

Benny I think that is what I have been doing as far as I know (setting up multiple domains). eg

On Wamp you edit the "hosts" file

127.0.0.1 localhost
127.0.0.1 mysilverstripe
127.0.0.1 subsite1.mysilverstripe

and then edit httpd-vhosts.conf

and add in a <VirtualHost> chunk for each domain, or use the serveralias tag also

<VirtualHost *:80>
ServerAdmin webmaster@localhost
DocumentRoot "f:/wamp/www/silverstripe/silverstripe-v2.4.0-rc2"
ServerName mysilverstripe
ErrorLog "logs/mysilverstripe.log"
CustomLog "logs/mysilverstripe.log" common
   
<directory "f:/wamp/www/silverstripe/silverstripe-v2.4.0-rc2">
Options Indexes FollowSymLinks
AllowOverride all
Order Deny,Allow
Deny from all
Allow from 127.0.0.1
</directory>

</VirtualHost>

<VirtualHost *:80>
ServerAdmin webmaster@localhost
DocumentRoot "f:/wamp/www/silverstripe/silverstripe-v2.4.0-rc2"
ServerName subsite1.mysilverstripe
ErrorLog "logs/mysilverstripe.log"
CustomLog "logs/mysilverstripe.log" common
   
<directory "f:/wamp/www/silverstripe/silverstripe-v2.4.0-rc2">
Options Indexes FollowSymLinks
AllowOverride all
Order Deny,Allow
Deny from all
Allow from 127.0.0.1
</directory>

</VirtualHost>

now when I go to

mysilverstripe or subsite1.mysilverstripe they both go to the same main home page of the silverstripe site.

Any ideas?

bennylope because I am on the grid service I don't have access to vhost.conf and MT have just said to use the .htaccess file

So I presume your working setup will not function for me... Does that mean I am out of options for getting this thing to run correctly?
I mean I guess I could always just create a subsites.mydomain.com directory and then create a file that redirects to the subsites page eg:
http://mydomain.com/subhome?SubsiteID=1

It kind of makes it difficult for when someone makes a subsite though as I would have to go and create this redirect manually, not something I really want to be doing actually.

I have tried to contact Sam the guy that wrote the subsites module and some of the other Silverstripe developers but I haven't been able to get any assistance.

Any other ideas?

Bennylope I have not tried what you suggested in your last post, but back trying to get my WAMP to run it, to best show you my setup I have collated an image together showing the screenshots of what my subsites setup looks like.

http://www.flickr.com/photos/42659897@N08/4597647580/sizes/l/

WillR said that getting subdomains to resolve are the bulk of peoples troubles with the module and to go through the subsite.php and debug the getSubsiteID function to find out what is going wrong.

I've done my best to try and get some information from the variables to work on what is going on and atempt to do some cross checking but I don't seem to be getting to far with it, all

#Debug::show($host); gives me is subsite1.mysilverstripe

Got any ideas on what or how I should be debugging this to work out what is going on?

/**
    * Get a matching subsite for the given host, or for the current HTTP_HOST.
    *
    * @param $host The host to find the subsite for. If not specified, $_SERVER['HTTP_HOST']
    * is used.
    *
    * @return int Subsite ID
    */
   static function getSubsiteIDForDomain($host = null, $returnMainIfNotFound = true) {
      
         
      if($host == null) $host = $_SERVER['HTTP_HOST'];      
      
      $host = str_replace('www.','',$host);
      $SQL_host = Convert::raw2sql($host);
      

      $matchingDomains = DataObject::get("SubsiteDomain", "'$SQL_host' LIKE replace(\"SubsiteDomain\".\"Domain\",'*','%')",
         "\"IsPrimary\" DESC", "INNER JOIN \"Subsite\" ON \"Subsite\".\"ID\" = \"SubsiteDomain\".\"SubsiteID\" AND
         \"Subsite\".\"IsPublic\"=1");
   
      if($matchingDomains) {
         $subsiteIDs = array_unique($matchingDomains->column('SubsiteID'));
         if(sizeof($subsiteIDs) > 1) user_error("Multiple subsites match '$host'", E_USER_WARNING);
         return $subsiteIDs[0];
      }
   
      // Check for a 'default' subsite
      if ($default = DataObject::get_one('Subsite', "\"DefaultSite\" = 1")) {
         return $default->ID;
      }
                  
      // Default subsite id = 0, the main site
      return 0;

Another related function

/**
    * This function gets the current subsite ID from the session. It used in the backend so Ajax requests
    * use the correct subsite. The frontend handles subsites differently. It calls getSubsiteIDForDomain
    * directly from ModelAsController::getNestedController. Only gets Subsite instances which have their
    * {@link IsPublic} flag set to TRUE.
    *
    * You can simulate subsite access without creating virtual hosts by appending ?SubsiteID=<ID> to the request.
    *
    * @todo Pass $request object from controller so we don't have to rely on $_REQUEST
    *
    * @param boolean $cache
    * @return int ID of the current subsite instance
    */
   static function currentSubsiteID() {      
      if(isset($_REQUEST['SubsiteID'])) $id = (int)$_REQUEST['SubsiteID'];
      else $id = Session::get('SubsiteID');

      if($id === NULL) {
         $id = self::getSubsiteIDForDomain();
         Session::set('SubsiteID', $id);
      }

      return (int)$id;
   }

Did you try doing this at all???