Cosme

I'm a rather small person. Currently I ride a 48 cm steel frame. I weigh in at about 110 lbs.

Because of my light weight, should I stick to a steel frame when upgrading? Or should I go for the absolutely lightest set-up and consider a carbon frame?

I came across some Dura-Ace 7702 components, so I'm pretty flexible when it comes to paying for my frame and fork. I'm considering spending around $1,000.

Lately I've considered the 2009 Salsa Pistola (steel), 2009 Specialized Allez (aluminum), and 2007 Kestrel Talon (carbon) that I found on the cheap.

Rustyoldbikes

The material a frame is made from is not very important. Most important is a good fit, which includes both the height of the frame, and the length of the frame. Spend some time at the bike shops in your neighborhood looking at their bikes, and getting fitting suggestions. If you end up buying a used bike, have your neighborhood bike shop tune it up, and buy a good lock and good front and rear lights to help compensate the shop for the time the staff invested in helping you get a proper fit.

MichaelW

Bike frames produced in a factory have to be a certain strength to cope with whoever rides it so lightweight riders end up with over-built bikes. Custom bikes can be made from much lighter grades of material (steel, Al or carbon) but the lightest production bikes are hard to beat in terms of weight.
If you look at the weight-weenies website you can see the frames that people start with to built ultra-light.
Weight is only a big consideration if you ride a lot of steep hills or big mountains. On the flat, aerodynamics play a greater role in going fast and over long distances, comfort is the primary factor. It is however, always nicer for us skinny riders to be matched to skinny bikes.