Hmmm, can I ask why you want to run Gnome on a server? Gnome is a desktop environment.
Anywayyyyy, if you want to install plain Debian you'll need all your machine's hardware details. Chipset, network card, scsi controller if it has one, video and audio if you'll be using them, all the hardware it has. This is one of the advantages of using Morphix and GNOPPIX to install Debian: they have hardware detection. So making sure you have all that info is your first step.
Step two depends on how you want to install, do you have Debian CDs already? If you don't, and you're on a fat pipe, a net install CD is probably the way to go.
A lot will depend on what you actually want to use the machine for. What services are you going to be running, for how many users, will it be an internal server or publicly accessible?
Some more info on what you want to do with the machine would help.
~~~
Steve