I use a running machine at my local gym and I occasionally go for a run near where I live. I usually do about 5 km in about half an hour - I'm no Paula Radcliffe! Running nude is a nice idea, but if you're going to run for more than a few minutes you'll find it very uncomfortable. I'm an a cup, and just about the only time I wear a bra is for exercise. I read an interview with Nigella Lawson and she said that she has her own private gym and does her workout wearing nothing but trainers and a sports bra - sadly, I couldn't get away with that at my local gym! As for trainers, go to a good sports shop and try a few different pairs, and get some advice from the people who work there. As TJG said, it's a good idea to have 2 pairs - my current favourites are Adidas.