I have this rule:
RewriteRule ^(about|installation|mypages|privacy|terms)(/)*$
/index.php?kind=portal&id=1&page=$1&%{QUERY_STRING} [L]
How can I change it so that it would work only for a specific domain, www.domain.com
for example?
You need a rewrite condition:
RewriteCond %{HTTP_HOST} ^www.domain.com$
before your rewrite rule.
If you list several rewrite conditions before your rules, everyone of them must match for the RewriteRule to be executed, for example:
RewriteCond %{HTTP_HOST} ^www.domain.com$
RewriteCond %{HTTP_HOST} ^www.domain2.com$
which will of course NOT work, because the HTTP_HOST cannot contain simultaneously both values.
You must then use the [OR] modifier:
RewriteCond %{HTTP_HOST} ^www.domain.com$ [OR]
RewriteCond %{HTTP_HOST} ^www.domain2.com$
so that the RewriteRule is executed if ANY of the above conditions match.
See http://httpd.apache.org/docs/2.0/mod/mod_rewrite.html#rewritecond for more information.