This site is probably the best place to read up on the various models. The 1750 is favoured by some because the dash, grill and lights styling is a bit nicer than the 2lt, and as mentioned above it's considered a bit more free revving, but the 2lt has more torque.
If you know nothing about 105s, there are some good books around that give a rundown on the different versions. The buyers guide by Keith Booker is not a bad read for a novice, and includes plenty of tips on what to look out for when buying a 105. You'll find it on ebay pretty cheap, or on most motoring book websites.