Hi,
If you're talking about vhosts on the same box, you can use mod_rewrite to rewrite foo.com to bar.com, while actually bar.com is an alias of foo.com? If you're using apache, something like the following should do:
Code:
...
ServerName foo.com
ServerAlias bar/com
RewriteCond %{HTTP_HOST} !^bar.com
RewriteRule (.*) http://bar.com/$1
...
In case that the 2 hosts are on different boxes you can setup bar.com as a reverse proxy of foo.com
Regards