point domain to a sub

Hello
Which script do you people recommend for domain redirection. I need to point several domain names to different sub directories of my site. My host does allow multiple domain names to point to my site but I need to use a script on my site to redirect the domain names to the subs. I have found several scripts that do this but do not know which is best. I do want the domain name to show not the sub name.

Or would it be best to use one of the FREE domain name redirect services? And do they offer pointing of the names to a sub directory?

Thanks for any help!
Larry Davis