Don't think, just do it.
You will not regret it.
Neither will you sleep again, pass any more exams, have a social life more than 12 foot from your TV, be able to turn it off.
Get a box, get live & get playing.
Some other games will be your next big priority in life, forget food (except pizza & beer).
The cost of the DVD kit here in the UK is almost as much as a DVD player & a standalone player is much better for watching DVD's as they do not make as much noise.
If your into first person shooters (FPS) then Get Rainbow Six 3 & Ghost Recon: Island Thunder to warm you up till Rainbow Six: Black Arrow comes out next month.
A pair of big headphones are handy on FPS games, help you to hear exactly where footsteps are coming from.
The Xbox does not require knowledge, it requires constant playing & short breaks.
Oh and a lavatory pretty close.
P.S. think long and hard about your gamertag, you cannot change it once chosen & "sniper" & "commanderinchief" types are so boring & common, "Jerrek" on the other hand would be good.