need help installing jjos 3.12 from os2.12

I downloaded jjos 3.12 for the first time and followed all the instructions and I'm getting this messege when I turn the MPC back on:

A correct OS file wasn't found.
system halt......


I tried holding the "window" button when turning on a the "erase" button but nothing seems to work. Do I need jjos 3.08 (which I can't find anywhere)?

nevermind, I realised that the os didn't download all the way. Should have made sure to look at the size of the file. Thanks anyways...