Skill Learning Question

I'm trying to make a thing where the player learns skills by getting books(like tomes and such).

But the problem is that I want the player to be a certain level to learn it.

Example: you buy a book to learn a skill but you need to be lvl 5 or higher to learn it.

Any help would be appreciated

What RPGMaker are you using? XP? VX? R2k/2k3?

I am using XP

http://rmrk.net/index.php/topic,33002.0.html

In the future, try to post in the correct board please.

Thank you