I've installed cPanel coupple years ago.
Basicly everything You need to know is on cpanel.net.
First You'll need a clean server. The only thing You have to have is a fresh compatible system and download cPanel/WHM (it's the same package) and run the installer, which will do most things for You. It will ask questions so be prepared.
You can buy a license here: http://cpanel.net/products/cpanelwhm...-products.html
but it's even better to get a trial before You buy so You can setup everything and see what You're buying. You'll need two DNS servers for everything to work automatically (one with cPanel and the second with a cPanel DNS addon which will automatically replicate the dns zones on both servers.
Here are the system requirements: http://cpanel.net/products/cpanelwhm...uirements.html
Setting up RAID and/or LVM now will also be helpful in the future.