I have mydomain.com and mydomain.net on different virtual hosting accounts. I use mydomain.com as my main account.
I want to use mydomain.net as additional bandwidth.
How do I link to mydomain.net but not resolve that in the browser so that although I go to mydomain.net, it still shows to the user as mydomain.com in the browser.
Using WHM/CPanel with the domains.

Set it up so mydomain.com simply opens mydomain.net in a full size frame in the browser.

Same thing http://www.mydomain.com does for stealth website redirection :)

most of the dns companies that house domains can do this some for free....check ultradns.com, www.powerdns.com, easydns.com etc