Here is some information that I have written down about estimating calorie amounts. I am a calorie counter myself and I find that it is fairly simple.
The first thing to figure out is you basal metabolic rate. This is esentially the amount of calories that your body uses just to stay alive if you do not do any activity. I have seen several estimators, but one that I rather like is weight in kilograms (which is pounds divided by 2.2) multiplied by .9 and the result is multiplied by 24. this is an estimate of your BMR. Of course your body also burns calories everytime you move and when you are digesting food (thermic effect). So, if you take your BMR and multiply it by an activity factor (1.3 for sedintary, 1.5 for light, 1.7 for moderate and 1.9 for heavy activity) you can come up with a rough estimate for how many calories your body is using in a day. If you are looking to maintain this is what you eat. However, if you want to lose weight you eat less. Since healty, sustainable weight loss is about a pound a week, if you eat aproximately 500 calories less than you use you will lose at a healthy rate. However, it is also important not to have your body go into starvation mode becuase then you metabolism slows way down. Generally this happens when you eat too few calories. I have heard the number 1200 bandied about as the number you do not want to go below, but of course this will vary depending on how much you weigh and how much you exercise. I do not remember exactaly where I got this formula from, but it is working out ok for me.
You might want to check out the doing it the old fashioned way thread beucasee it is full of wacky eat right and exercise types )like me). I personally eat right, but the exercise thing is always a struggle for me.
I hope this helps a bit.