The series "Conway's History of the Ship" makes an excellent starting point for virtually any research project in the history of naval architecture or shipbuilding. It originally consisted of 12 volumes, all hardbound; as I remember they originally cost $50 apiece or thereabouts. I managed to pick up all of them - over a period of several years. Shortly after I bought the last one, of course, the series came back in paperback for about $35 per volume.
The two volumes that deal with the period RTimmer's interested in are The Earliest Ships and Cogs, Caravels and Galleons: The Sailing Ship, 1000-1650. The first name covers Viking ships, among many other topics (including non-Western vessels, which the rest of the series ignores for the most part). The second is self-explanatory. I found The Earliest Ships on the Conway website - for an excellent price: http://www.anovabooks.com/products/product.asp?catId=10&subcatId=42&id=322 . Cogs, Caravels and Galleons appears to be out of print; the best I could find in a few minutes' surfing were some used copies at Amazon, for prices that are pretty outrageous: http://www.amazon.com/Cogs-Caravels-Galleons-Sailing-1000-1650/dp/0785812652/ref=sr_1_1?ie=UTF8&s=books&qid=1266429390&sr=1-1 .
Anyway, that's what I'd recommend for a start. That whole series is excellent as an introduction to the subject as it was understood when the books were written - the 1990s, as I remember (I'd have to check the books themselves to get the exact dates). Each volume has an extensive bibliography, which is an excellent starting point for future digging.
Hope that helps a little.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.