T.F.
if you swaddle right, you don't need special swaddle blankets, but they can make doing it easier! However, the special swaddle blankets also are often too thick and warm for this region and type of year, so be aware of that when buying!
For best iformation, watch "The happiest baby on the block" by Dr. Harvy Karp" DVD (you can rent, borrow or buy on line or locally) and watch the question and anser part as well as the "show" to to get the technique down and to learn that swaddling is only the first step in a happy baby!
Best of luck!
T.