Downgrade Impossible

[iChuckles]

I have worked on this for two days with no success. I have a 3gs that i made the mistake of upgrading to the 4.3 firmware. Now need to downgrade to 4.2 or less to JB. Well I know others have the same issue I have, but NO answers I have found actually work.
I have downloaded .zip firmware files time and again and there are no .ISPW files in them. Shift+Restore in Itunes wants an .ISPW file, and an .ISPW file only. I have seached the web and you CANNOT download this file type . I am running XP and I have gone to folder options and unhidden files and folders, unchecked system folders etc. There is no .ispw file on my pc, and can't find anyone who has given a legit answer as to how to get one.
I have tried to JB using GP0n, but it just wouldn't work. JBme, wouldnt work because I am running 4.3 FW, so assume thats why GP0n didn't work.
I am at a total loss as to what to do to get this iPhone JB'n, and can't seem to get legit answers from anyone as to what/How to do. I have found numerous forums and boards with others who have given up as well, so I am all ears, anyone??

[i.Annie]

Rename the .zip file to .ipsw

Or download the same file again with firefox or chrome.

You also need SHSHs to downgrade, so be sure you have those. Check with TinyUmbrella.

If you don't have SHSHs you can't downgrade.

Edit: don't unzip the .zip file. You'll probably need to download it again, just make sure to use one of the browsers I listed.

You probably used Internet Explorer which doesn't download the firmwares in the right format.

[iChuckles]

"Thanks Annie for the speedy reply. I have tiny umblella and have the 4.1 SHSH blob but don't see how to save it to my PC, or how to get Itunes to see it. I have tried, I assure you.
So if I download the "iPhone2,1_4.1_8B117_Restore.zip" file, rename it as is with an ".ispw" ext I can use this file to downgrade in itunes?

Was to quick to hit enter. I have downloaded Firefox and will try the steps you suggest. Will post a follow up when done

[i.Annie]

Since you said you have SHSHs for 4.1, just follow the following steps.

Run TinyUmbrella

Click Save SHSHs

Click Start TSS Server

Open iTunes

Shift+restore to your stock 4.1 ipsw

Receive error 1015

Use TinyUmbrella to exit recovery mode

Jailbreak as normal. I recommend Redsn0w 0.9.6rc8

[iChuckles]

Annie I love ya!!! After two day of misery I finally have a jailbroken 3GS. And once again all that hassle was due to the MS empire with IE not downloading file like the rest of the world. I will have a MAC within a month now, and Bye Bye to Big Brother for me.
So here are the steps I had to take on my journey:

Use FireFox (Not IE)
Downloaded 4.1 Firmware (I used iphoneheat.comP)
From itunes Shift+ Restore
Select the .ISPW file you downloaded from the location you saved it to
Note: I just left the Firefox downloads window open and drug the file to my desktop
Itunes finished and left my phone in recovery mode (error 1015)
Open Tiny Umbrella (or download it if needed)
Started TSS servers
Selected my device from left menu
Click exit recovery mode button
DONE!
Went to Settings/General/About --- Version - 4.1 (or whatever version you downloaded/used)
Turned off my phone
Started redsn0w_win_0.9.6rc8
The rest will be following instructions

Thanks to i.Annie for getting me started, and hope this helps some of you out.

Next -- Unlocking!

[i.Annie]

I'm glad you got your downgrade to happen

[mortopher]

Do you have an old or new bootrom?

[iChuckles]

OK No not finished, stuck again!
After my jailbreak all was well, PDowngrade complete, Cydia installed, everything seemed fine.
Problem:
No contacts, old software etc.
So I launch iTunes (to restore from the backup I did before the JB)
I hit Restore and iTunes gives me a can't restore message "Software to Old"
So I run it as a new device
Restore factory settings
And the only option then is Update and restore
Did that
Now I am right back where I Started
Version 4.3
No Cydia
Jailbreak lost
Now no idea how to get jailbroken and keep my contacts etc.
Any ideas anyone?

[i.Annie]

Did you get my PM? I covered the contacts issue.

[iChuckles]

Yes I did but wouldn't work. The steps I took i listed here, and iTunes just would not play along. Not sure if I should start over with 4.1 or not. Got to have contacts at a minimum