Legacy Xcode
So you want to make new apps for an out of date system do you? This is the place for them resources and info.
Something you need to be aware of if you are going to join this battle against time; The weapons of choice are of course are the actual legacy devices that this software was originally meant for. This time frame of tech is notoriously finicky even if you have the best emulation setup around. You're gonna want an aluminum body mac, built between the years 2007 and 2012. Not sure why things are the way they are but things will go a lot easier for you if you abide by this. Next you gotta make sure you're running 10.6 or 10.7. For fidelity; I'm running 10.7.5 so if something doesn't work for you, try again with my setup before claiming your melons are rotten.
Apple has always been hard to work with when it comes to getting old or closed source resources. That being said, if you have a developer account, they will allow you to download what you need- but not without jumping through some hoops. One resource I've come across that makes clearing these hoops a little bit easier has been the Xcode Releases page. It's a directory that will link you to the Apple hosted DMG's but you will need to sign in with your developer account to gain access. If you say "heck off" to all that noise and just want the old releases, you can find it in my Downloads page.
Installation:
Okay so you've got your late 2000's Mac and it's running 10.6 or 10.7. Great! Now you need Xcode 3.2.6. This Xcode was the last release before iOS 3 support was dropped in versions 4+. If you are attempting to make iOS 3 apps in Xcode 4 or above, you will surely fail. In order to have Xcode successfully install, you need to make sure any newer versions are all completely uninstalled and deleted. If you are trapped in some kind of an install/uninstall loop at this stage, I recommend restarting after your uninstall & restarting after your reinstall.
Usage
*I am currently writing this portion, check back in a bit*