What's your anticipated OG? Are planning on using a single pack of dry or liquid yeast?
If you're under 1.085 you could probably get away with a single pack of rehydrated dry yeast for a 2 gal batch. If you're using liquid yeast I would recommend doing a small starter. I do mostly 2.5 gallon batches and on some of my higher gravity belgiums I've done quart-2 quart starters (decanting before adding).
The general rule is that the higher the gravity the greater the number of healthy yeast cells are required for good fermentation. Mr. Malty
is a good place to check pitching rates and to make sure you have adequate yeast.