Mac Forums

I was trying to erase my hard drive but I ended up clicking on erase free space in utilities. I wasn't sure what it was so I let it do it's thing. Halfway through I clicked on skip so it didn't finish erasing free space. The next day I popped in the Mac OS X install dvd to try and make my mac back to factory settings but every time I click on Erase for my hard drive, it says that it can't unmount. What happened?

I've barely downloaded anything to my mac and it is supposed to have almost all 500 gigs, but now it says that there are only 250 gigs available. Could someone explain to me what I did and how to solve it?

I have a Mac OS X version 10.6.3

I'm still learning how to use it, I appreciate your help.
hey it's cool that you guys are actually responding.. but I'd appreciate if you also answer with a solution to this problem too. I'm here because I need your help on something I don't know much about. Thanks. And yeah man, I know I messed up, I just wanna fix it.