Well...it really depends on a whole lot of things - how much you exercise...the level of your exercise...etc.
If you check the Web there are several BMR calculators (Basal Metabolic Rate that is!) that you can use to get a GENERAL idea of how many calories you should be taken in. But remember, it's not just the calories, it's the quality of the food you eat. The more lean proteins, complex carbs, veggies and the less processed foods you eat, the better for fat loss.
Krista Scott Dixon has a great article called "Dieting 101" right here
http://www.stumptuous.com/dietsdontwork.html that you might want to check out...
Also, a new gadget has come onto the market called the BodyGem which apparently measures your BMR through a breathalyzer. I'm still holding out judgement on it until I hear more since it's a fairly new development - here's their website:
http://www.healthetech.com/corp/info/met_bodygem.jsp A couple of gals at the Ladies Who Lift forum have had the test done...hope that helps a bit...