hi,
Not exactly sure of the solution, but this can be done either at the host DNS level, updating the Server A Record and CNAME / alias (best done by your hosting company). Second way is by use of redirects using .htaccess (google got references to get this done).
you can ask your host to make the domain access with or without www (even for subdomains), they got the configs for that i presume. I got it done around 4 years back for one of my site. I was hosted on lunarpages.com. They did it for me.
Lastly, there might be simpler way of doing it, If you get to know any, please enlighten me too then.
Regards
Arvind