OK, I'm 6 foot tall and I weigh 215 pounds. Based on my weight when I was younger (I'm in my late thirties), I'd say I'm about 25 to 30 pounds overweight (fat) now. I started lifting about three weeks ago, and I'm already seeing a slight increase in strength, tone and size. My question is this: Because I'm already a little overweight, can I keep my caloric intake the same for a while? Would the amount of calories I consume go more toward muscle production rather than the accumulation of fat now that I'm working out? I'd hate to gain more fat in an attempt to feed newly developed muscle. I'm sure I will have to boost calories at some point in the future if my muscles continue to grow, but, for now, am I good?
That depends on how much (and to some extent what) you're eating now.
Generally speaking, you'll gain muscle if you're eating "at maintenance" or slightly above (usually, around 100-200 calories). However, you could be eating way more if you don't know what your maintenance calories are to begin with.
There are a number of different ways you can calculate your calorie needs, and a dozen different calculators online (here's one using the Harris Benedict formula). For your size, that calculator puts your requirements at about 2300 for a sedentary lifestyle. If you're eating about that, you should be fine for the most part, just make sure you're actually eating about there (people are notoriously bad at estimating how much they actually eat, so it's a good idea to spend a couple of weeks measuring and tracking your food).
Additionally, you'll want to take a good look at your diet. While you may be seeing muscle gains now, that's likely "newbie gains," which will taper off pretty quickly. If you want to continue to gain muscle (and lose fat during "cut" phases), you'll need to adjust your diet accordingly. You probably won't get far if you're living off of pasta and potatoes. Make sure you're getting enough protein, first and foremost - between .5 and 1g per pound of lean body mass, depending on how much you're working out, and don't go crazy on the carbs (remember, you're a lifter, not a runner, you don't need tons of quick-access energy).
From there, you'll want to monitor not just your weight, but your body composition (your body fat percentage), to make sure that the gains you make are, in fact, muscle. There are a number of ways you can do this, with varying degrees of accuracy, but for the most part, the important part is consistency in its numbers (ie - if a measurement is 5% high, as long as its 5% high all the time, it can still serve as a way to track progress). As your weight and body fat percentage changes, you'll want to revisit your calorie needs calculator to make sure that you're still on target, as you may need more (or less!) to sustain your body.