I have read quite a few topics addressing this problem lately and I have this problem as well. I have a late 2008 MacBook (5,1) and I cannot manage to make a clean install with ML. In fact, I cannot make a clean install with Snow Leopard or Lion. It only allows me to make a clean install with Leopard (that was the OSX version my MacBook came originally with when I bought it). Can someone finally clarify this issue for me and for all the others that seam to be having the same issue? Please? Don't come here saying I'm doing something wrong with my bootable USB stick. For sure I'm doing something wrong, you don't need to tell me that. I rather read from you what I'm doing wrong and how to fix it in order to make a clean install with Mountain Lion. Thank you!