That's it, toss a couple of scoops into a blender (or use a stick blender) and maybe a cup of whole milk. Low-fat or skim milk won't be as creamy, but will work. If you want it sinfully rich, use light cream or half-and-half cream. I've had better luck using the stick blender - more control. Don't over-blend it.
You can use plain vanilla ice cream and coffee syrup along with the milk if you want to. With the coffee syrup you can make it as strong or as mild as you want. It could be cheaper in the end than Starbucks, and who knows, you might like it better.
If you want booze in it, add some vodka and Kahlua. If you leave out the ice cream and use light cream (but no added coffee syrup), serving over some ice, that's a White Russian. Pretty tasty on a hot day.
Coffee syrup is a specialty of the southeastern Massachusetts and Rhode Island area. You can get a coffee shake or coffee milk just about anywhere around there, including McDonalds. You can't toss a brick without hitting someplace you can buy coffee ice cream either.
Morgan is right - I do that too instead of buying syrup. Make up some strong coffee in whatever roast you like (Starbucks house blend?). Brew a 10-12 cup pot, pour off into a sealable screw-top container (I use a Nalgene bottle) and add about 1/2-1 cup of sugar to it. Shake it up a bit to dissolve the sugar, then let cool in fridge. This is also good all on its own as a quick and dirty iced-coffee. I make it all the time in the hot weather.