subdomains, does it has to work like that

example vhost conf

Code:

######################################
# Vhost: www.domain.tld:80
######################################
#
#
<VirtualHost IP_ADDRESS:80>
	ServerName www.domain.tld:80
	ServerAdmin [email protected]
	DocumentRoot /var/www/web34/web
	ServerAlias domain.tld forum.domain.tld www.forum.domain.tld www.domain.tld
	DirectoryIndex index.html index.htm index.php index.php5 index.php4 index.php3 index.shtml index.cgi index.tld index.jsp Default.htm default.htm
	Alias  /cgi-bin/ /var/www/web34/cgi-bin/
	AddHandler cgi-script .cgi
	AddHandler cgi-script .pl
	ErrorLog /var/www/web34/log/error.log
	AddType aptldication/x-httpd-php .php .php3 .php4 .php5
	php_admin_flag safe_mode Off
	AddType text/html .shtml
	AddOutputFilter INCLUDES .shtml
	Alias /error/ "/var/www/web34/web/error/"
	ErrorDocument 400 /error/invalidSyntax.html
	ErrorDocument 401 /error/authorizationRequired.html
	ErrorDocument 403 /error/forbidden.html
	ErrorDocument 404 /error/fileNotFound.html
	ErrorDocument 405 /error/methodNotAllowed.html
	ErrorDocument 500 /error/internalServerError.html
	ErrorDocument 503 /error/overloaded.html
	AliasMatch ^/~([^/]+)(/(.*))? /var/www/web34/user/$1/web/$3
	AliasMatch ^/users/([^/]+)(/(.*))? /var/www/web34/user/$1/web/$3
	RewriteEngine on
	RewriteCond %{HTTP_HOST}   ^forum\.domain\.tld [NC]
	RewriteRule   ^/(.*)$  http://www.domain.tld/forum$1  [R]
	RewriteCond %{HTTP_HOST}   ^www\.forum\.domain\.tld [NC]
	RewriteRule   ^/(.*)$  http://www.domain.tld/forum$1  [R]
	<IfModule mod_rewrite.c>
	  RewriteEngine on
	  RewriteCond %{REQUEST_METHOD} ^(TRACE|TRACK)
	  RewriteRule .* - [F]
	</IfModule>
</VirtualHost>
#
#
#
######################################

and now. entering address forum.domain.tld i'm redirected to the domain.tld/forum . I'm moving my two virtual hostings into vps with isp2 and it drives me mad. I'm used to that when i create a subdomain the subdomain stays in address bar. Is it connected with this rewrite cond? Is it possible to change isp2 files to make as I soopose other vhosts with subdomains?
I dont need "other way to get into subfolder", and creating completely new sites isn't that what i wish to have...

 

thanks for response ;]

i think that the thing which i wanted to have are multiple Document roots in domain. For example

I create new Site, space i 1000MB, Traffic 60GB/y

and i connect to this portal domain www.domain.tld. That portal has forum located at www.domain.tld/forum BUT I want the forum to bo placed under www.forum.domain.tld. Actually attaching such co-domain, and redirecting it, the browswer redirects me into www.domain.tld/forum. So when I'll print a $_SERVER['HTTP_HOST'] i'll get domain.tld not forum.domain.tld.

Does this is managed by rewrite rules too ? If yes where are the base patterns - php files- in isp2 with wchich i can change those things?