Thank you, WoodyZ! You really helped me alot there!
Well, about that "very tricky installation" statement: I was confused by the window popping up at first because when I clicked on the customize settings, I could only change the directory of the virtual machine and wasn't aware that the other settings like the space the virtual disk is going to take could be changed after choosing the directory so I thought the only thing one could choose is the directory. 
Also, GrandPerspective really is a great program. I've already been using it and it's a lot easier to manage the whole disk space.