This is a repeat of a post I did a week or two ago to someone who had the same questions:
The types of weights you need to start with will totally depend on your current abilities. When I started I had a pair of 3 lb dumbells, a pair of 5 lbs, and a pair of 8 lbs. You may need lighter or heavier weights, but that's a typical set up for a woman just starting out.
I can point you to a bunch of different resources that I've found helpful, and others here will have other recommendations.
I really like Kathy Smith's video series called Lift Weights to Lose Weight. I think the original version would be a great place to start -- it contains a 20-minute upper body and a 20-minute lower body workout. You could do both on the same day, and do it 2 or 3 times per week (resting a day in between). Or, you could do upper body one day, lower body the next, for either 4 or 6 days per week. This is in addition to the cardio you might do. The routines are well-designed and she gives good instruction on form. When you've worked with this tape for a while you could move up to the innovative volume 2. (You can also start out with volume 2, it's just a little more challenging). She also has a book with the same title that gives great explanations about why weight lifting is important and general information, along with specific exercises.
There is also a great online reference at www.stumptuous.com/weights.html
if you are more of a do-it-yourselfer. TONS of great info and inspiration there.