No you can learn certain skills upto a higher level than 5. All it needs is a teacher that teaches you thhose higher levels.
but is it possible that if you learned a lockpick skill to level 5, you still can upgrade to level 6 with an aditional skill point?
All of your skills start with a maximum level of 0. Your elected class skills (from character creation) are set to a maximum of level 5. When you learn something, such as the Elemental spells from Edmund, he increases your maximum to the stated level.
So with your lockpick example, you could not spend a sixth skill point in Lockpicking unless you found a teacher that could teach you how to train up to level 6 first. The teacher gives you the theory, then you practince.
We can all (once of age) drive a car, and practice getting better at it, but we would never be able to drive in a professional race without advanced driving training, and then practice as well.
rocked! 
is very buggy
