Sarlat driving

I suggest you get Rick's Dordogne guidebook, if you don't already have it, and a good detailed regional map (Amazon.com?). Rick's guide has driving routes encompassing the major sights, and you should be able to cover most in two days.

I second the recommendation, look at the guidebook (or any good one) and decide what you want to see, then find those places on a map and plan your route for each day. A car is definitely the way to see this area if you can. We enjoyed the Lascaux II and Font-de-Gaume caves, the prehistory museum at Les Eyzies, the castles at Beynac and Castelnaud, the hilltop town of Domme, the cliffside towns of La Roque-Gageac and Rocamadour, the larger city of Cahors, and points in between, but we had four full days. Sarlat itself of course has many sights and a great market twice a week.

Castles and caves are the main attractions, you can mix and match. I've heard from many, on this board and elsewhere, that Peche-Merle is on balance the best cave and I hope to visit someday. I'd like to see also Perigeux and Bergerac. So no lack of opportunities, you just have to set your priorities and find the most efficient routes. Bear in mind that driving on these country roads, while very scenic and rewarding, will take longer than the equivalent distances in the US. Via Michelin is a helpful planning tool but tends to underestimate actual drive times.