Yes, the graphics card is unimportant in a server, all it needs a a good CPU, RAM, disk transfer rate, and a fast upload speed
. (I used to host game servers myself, in addition to Teamspeak(which I still host))
Halo:CE wont require much CPU/RAM wise so even a box thats a few years old should be good.
I double checked it on the web.http://dedicatedhostingweb.org/does-a-better-graphics-card-a-better-dedicated-game-server
Says which I thought. Server graphics doesnt matter, allt he matters is the clients (gamers) graphics cards.
Norton 360 may end up being a hassle when making a server due to its "protection" and bottleneck it with active scanning and protection. If this is just a server and wont be browsing the web something like Microsoft Security Essestials would work great (its free).
Hope this solves all your questions!