I know reminds you of something else doesn't it? Seriously though, If I have 1 managed linux dedicated server (CentOS w/ cpanel v.11) and 1 managed windows dedicated server (Windows Server 2003 w/ Plesk 8) and want to the setup automatically through WHMCS under the same domain name (or appearance) how would I accomplish this task?

I know that I could simply add additional servers to the server configuration of 1 whmcs billing software installation. The problem is if I had to buy a separate domain for the other server and run them through 1 website it may appear shady to have the domain name change in the url during checkout.

I've seen few web hosts other both kinds of hosting through 1 website without redirecting to a different domain. If I have to have 2 different domains assigned to 2 different server boxes could I mask/cloak/I don't know the technical word for it so that the url appears as the same domain weather purchasing shared hosting for windows or linux?

You could use the .com on one, and the .net on the other.

I've seen this done before.

Sub-domain? Many hosts use a sub-domain during checkout.

Good point on the use of a subdomain, I completely overlooked the obvious

Each server just needs a sub-domain of your main domain for your main site, just stick an A-Record pointing sub-domain (hostname) to the servers IP.