Is there a possible way to update to 4.0 on an iPhone 3G without updating the baseband on Windows?

So right now my version is 3.1.2 and on a 05.12.01 I want to update the OS to 4.0 but I want to keep the baseband and I'm running off Windows. I know that you can do this on a Mac with Pwnage but how would you go about doing this on Windows?

Do you have a SHSH for iOS 4.0? Do you have any saved SHSH for 4.0 or higher?

Why iOS 4.0? it runs horribly on a 3G iPhone, reports are that 4.2.1 or 4.1 run much better on a 3G iPhone.

No I do not have any SHSH but I was referencing more towards the generalization of 4.0 OS including 4.1 or 4.2.1

We don't recommend or support any windows solution for what you want to do.
Borrow a mac for an hour. Build a virtual machine running OS X.

SHSH is very important to save (especially from iOS 4.1 and higher) - go and save your 4.2.1 SHSH via TinyUmbrella NOW, 4.3 will be out in a few days and then it will be too late.

The only windows software for custom IPSW is sn0wbreeze and we refuse to recommend it. It was a horribly unstable program originally and bricked a lot of early testers iPhones. It has got a bit better, but it is not reliable enough for us to recommend or support.

Could you give me a tutorial to save a SHSH? I am unfarmiliar with what and how this process is done

Could you search? Do some reading in the forums. The moderators explain this nearly every day... a quick search found the following replies.
http://www.hackint0sh.org/f247/14812...htm#post582883
http://www.hackint0sh.org/f266/21211...htm#post704752
http://www.hackint0sh.org/f266/19122...htm#post664481