You need several; here is my suggested list. For the rifles, I list them in order of increasing cost within the category.
1. Battle Rifle: M1 Garand, PTR91, FN FAL, or M1A/M14. Whatever you prefer.
2. Intermediate caliber rifle: SKS, AK, AR. Again, your preference.
3. Any decent .22 pistol, preferably Ruger. This is just so you can afford some range time. Oh, and buy a few cases of .22LR while you're at it... ammo prices are increasing rapidly.
4. 1911, BHP, CZ75, Sig... you need an all-steel pistol. My Taurus 1911SS is great.
5. Consider a shotgun. I'm no expert -- I have only one, a Mossberg 930 semi-auto... very reasonably priced and not a hiccup, even with cheap Wal-mart bulk ammo.