If your package supports multiple addon domains (special package etc) then all you have to do is the following...
Open Cpanel (linux) goto addon domains then enter the domain name eg: anyone4tea.com, put in a directory name eg: anyone4tea, and a password... Click add it will take about a min or so and you will have a new domain name...
Now for the fun part... lets say you have an account here using abc.com. you make an addon domain of xyz.com with the directory of xyz. the way they route things is cpanel makes a dns and apache entry for xyz.com.abc.com and www.xyz.com.abc.com that point to the new directory. so xyz.com will goto abc.com/xyz ... Some people have said this causes them to have duplicate entries in search engines, and reveals that the xyz.com domain is a addon of abc.com... so you use some rewriting in .htaccess files to fix that... one in the root of abc.com's public_html dir... this one says...
Redirect permanent /xyz
http://www.xyz.comThis will keep the search engines out of abc.com/xyz and force them to see it as www.xyz.com like you intended...
you can rewrite the url's some more to eliminate the xyz.com.abc.com as well....
Put this in .htaccess in the /xyz directory..:
RewriteEngine on
RewriteCond %{HTTP_HOST} ^www\.xyz\.com\.abc\.com [NC]
RewriteRule ^(.*)
http://www.xyz.com/$1 [R=301]
RewriteCond %{HTTP_HOST} ^xyz\.com\.abc\.com [NC]
RewriteRule ^(.*)
http://xyz.com/$1 [R=301]
Those last part will take the url of www.xyz.com.abc.com (the subdomains created by the process in cpanel) and route them to the proper URL to display of www.xyz.com, same for the xyz.com.abc.com and rewrite to xyz.com ...
Jason