where download dev tools 4.2?

Trying to set up my iPod touch (Again, never got it to work) with Apple's dev tools and Unity iPhone basic.

Have established that Apple's 4.3 version isn't working very well with Unity yet so trying to get 4.2. Can't find it on Apple's site. I've registered as a developer and all that but am new to iPhone and don't want more problems than I already have by downloading an IOS dev version that isn't well supported yet. Anyone point me to a link for dev 4.2? Thanks!