how hard is it to setup two power supply units in one computer? [Troubleshooting]

[Troubleshooting] i just purchased a graphic card and a new power supply. i have heard of people using two power supplies in one computer, and i'm wondering how hard a system like that would be to set up. any help would be appreciated.

Is this a good guide? http://www.overclock.net/t/15751/info-can-i-use-two-power-supplies-with-one-computer