I have the K100d, it's great but... I'm not sure it's the right choice for the kind of sports photography you'll be doing. While the K100d's continuous shooting rate is slightly faster than the D40 or D50s, the K100d has a shallower buffer than either which means it can take less shots at that rate before it slows down while writing to the card. The K100d allows for 3 RAW or 5 Jpeg shots at 2.8fps, while the D50 allows for 4 RAW or 12 Jpeg at 2.5fps, and the D40 allows for 9 RAW or unlimited Jpeg at the same rate... so from that point of view the D40 would possibly be best for shooting fast-moving sports, where you could be taking many continuous shots in order to get one image. On the other hand there are the drawbacks of the D40 already mentioned... the moral here is that there is no perfect camera, everything's a compromise especially if cost is an issue (and for most of us it always is).