If you play any player for 48 minutes (or more) at a position that is being trained, then they will get full training for the week, so you can get 6 players full training at 2 positions if each player gets exactly 48 minutes.
If a player gets minutes at a position that you are training, then their skills improve, even if you don't see any skills pop that week. A higher sublevel in a skill will make a player play better, so there is some benefit right away to whoever is being trained (even if the skill doesn't visibly increase that week). Regarding your last question, you can definately train a skill partially with one type of training, and then train it further (until it pops) with a different type of training.
I hope that helps :)
Last edited by The Mogul at 9/24/2009 10:06:46 PM