Hey Christian,
i'm glad to help. The program is coming along nicely. I hope i'll have time to check it deeply in the near future.
Btw, a little graphical glitch. If you resize the window, the Add Foder button and the Extract Selected Files button resizes themselves too. Maybe you should fix a minimun size for the window and when you maximize it the buttons remain in place but the part with the file names, lenght, etc. adapts to the new size. (But is not really important since the program works great)