i would like to use some classes that are into lib/Varien, my idea is to copy the classes into my project and put my classes to inherit from Varien's, actually i can do it, just using Ctrl-C and Ctrl-V. lol, what i really mean is if i do it, am i violating the copyright, law or maybe some license agreement of Magento?
EDIT: read Alan's post below. He is correct. While a profit-seeking venture should still consult a lawyer for any such project, there doesn't appear to be any issue with using the code for a personal project.
This isn't a programming question (rather, it is a legal question), but at least for the moment, let me say that those files are copyright of Magento Inc, and they reserve that copyright for those files. You do not have a legal right to copy those files into another project for you own use.
If you do copy them into your project, never try to sell it. Having taken their code, your code will have become a liability to any potential acquiring company.
Of course, I am not a lawyer, so if this is a big issue, feel free to contact one for more detailed information.