Hello,

It's actually possible to delete files from your hard drive using the OS X installation disk. However, you must use some Unix shell commands to accomplish this. After you've booted off the installation disk, from the Utilities menu, choose Terminal. I can give you a brief tutorial on how to delete files using Unix commands:

1. When working at the shell, always hit 'return' or 'enter' to execute the command that you've typed. To start with, run the following command:
   
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   cd "/Volumes"

   cd "/Volumes"
   This command changes the current directory to /Volumes.
2. Now, list the contents of this directory:
   
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   ls

   ls
3. Most likely it will list the name of your hard drive. Enter this directory by typing the following:
   
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   cd "Macintosh HD"

   cd "Macintosh HD"
   Or whatever name your hard drive is.
4. Now list the contents of your hard drive:
   
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   ls

   ls
   At this point, you should see the pattern. cd to a directory, and ls the contents. To go back (up) one directory use this command:
   
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   cd ..

   cd ..
5. With me so far? Now, go to a directory that contains files or folders you want to delete. To delete a file, do the following:
   
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   rm "essay.txt"

   rm "essay.txt"
   That command would delete a file named essay.txt .
6. Deleting an entire directory is similar:
   
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   rm -r "my directory"

   rm -r "my directory"
   That would delete a directory named my directory and all its contents.
7. When you're done, quit the Terminal, and you can continue installing OS X.

I hope that made sense. If you're confused, or have problems with the instructions, please ask, and I will do my best to further clarify them.