I am trying to update to OS 3.0.1 from 3.0 for my 3GS. I do not want to update to 3.1 in order to preserve the ability to jailbreak in the future. I downloaded the proper IPSW and shift-click on "Update" in iTunes to pull up the file (I have a PC). However, after extracting the file, I get the following error message: "This device isn't eligible for the requested build". Why is that? Is there a fix or am I doing something wrong?