My world was perfect when I had XCode version 3.x (3.1 or 3.2?).
Then one day, after upgrading my iPhone device to ios 4, i tried to deploy an app to my device. For some reason I thought that i needed XCode 4 (or SDK 4) in order to deploy directly to an ios 4.0 device (via xcode) because it was giving me an error(s) i've never seen before that seemed it was suggesting I upgrade XCode/SDK.

So now i have XCode 4.0 installed (build 4A304a) and am in a situation where I can't build my code, things are breaking left and right, and on top of it all I have to learn XCode all over again!!

Now here are my questions:

A) Do I need XCode 4 (and/or SDK 4) in order to deploy directly to an ios 4 device?

B) Do I have the right version of XCode?

C) I think there is a new Xcode version out, 4.02 or something. Should I get that right away?

D) Every time I download a new XCode, does it install "next" to the previous XCode versions? (it is a completely new XCode installation or does it upgrade any existing versions?)