iOS 5 to any previous iOS that will work with iTunes 9.2.1

[amy..]

I upgraded to iOS 5 recently (through my PC) on my 3GS but then got an iPhone 4s a few days later. I've passed my 3GS on to my girlfriend but her Mac won't allow her to update iTunes to 10.5 to sync with iOS 5. Stuck on iTunes 9.2.1 we are trying to install a previous version of iOS.

3GS in DFU mode, iTunes attempts to install iOS 4.0.1 - about 80% through I get a 1015 error. (The iPhone "iPhone" could not be restored. An unkown error occurred (1015).)
I have no interest in Jailbreaking and am utterly confused reading guides on restoring to an earlier version which all seem to contain conflicting info, but am I going to have to jailbreak to restore to earlier versions? Like I said, fully confused by all of this. Been trying for hours now!

I've also seen a lot of guides mentioning TinyUrabrella may be needed to overcome certain issues - this is also a problem as I went to download it and realised that too is only for OSX 10.5. Are there alternatives I could use?

Originally I followed a guide which had me edit the Hosts file, I have now removed the Apple line from the hosts file but still have the 1015 error.

Sorry for another 1015 post, I know there are plenty but I could do with this explaining a little and have a point in the right direction.

Thanks

[karli d]

I've finally fixed this by trying an iOS 4.1 restore through iTunes 10.5 on my PC. It reported a few other errors and then seemed to crash part way through, the phone then came on and when I restarted iTunes it prompted me to set up a new phone. Not sure how but one of those failed installs seemed to work.

I switched over to the Mac and set it up on there, all working great now. Just hope the sharables of a Mac can keep up with it now.