I own a cobalt raq4r
If i add a alias it is rewritten by the main domain of the site:

e.g.
main domain: www.domain.com
alias: www.mydomain.net

If i ask www.mydomain.net it is rewritten by www.domain.com

Is there a (easy) way to prevent the cobalt from doing this?
Mybe with .htaccess?

Well, for me what I did was go to httpd.conf and make the following modification :-

<VirtualHost xx.xx.xx.xx>
ServerName www.domain.com
ServerAdmin site1
DocumentRoot /home/sites/site1/web
ServerAlias domain.com
< Blah Blah Blah>
AliasMatch ^/~([^/]+)(/(.*))? /home/sites/site1/users/$1/web/$3

<VirtualHost xx.xx.xx.xx>
ServerName www.domain.net
ServerAdmin site1
DocumentRoot /home/sites/site1/web
ServerAlias domain.net
< Blah Blah Blah>
AliasMatch ^/~([^/]+)(/(.*))? /home/sites/site1/users/$1/web/$3

Basically just point the DocumentRoot and Alias Match to the same place and that should work.

So anything typing http://www.domain.com will get to http://www.domain.com and those to http://www.domain.net would get to http://www.domain.net . But the pages are aliases.

However, the stats would be screwed up because both would show the same consumption of bandwidth.

Hope that helps.

Maybe if you turn the rewrite off???