Which version of XCode should I download for mac OSx 10.6.8?
Officially, only old versions are supported, which can't be used for compiling for 5.1.1, let alone 6.0b. However, you can easily hack even the latest Xcode versions to run under SL:
Excerpt from
http://www.cocoabuilder.com/archive/xcode/315055-ios-5-1-sdk-for-xcode-4-2-for-snow-leopard.html :
From the Dev Forum Link
"I for one can't upgrade to Lion as I have stuff in my environment which apparently breaks under Lion. So rather than restore my devices to 5.0.1 and all the hassle that involves, I put my hacking hat on and came up with the following solution.
It presumes your current XCode 4.2 installation is in /Developer, and make sure XCode is NOT running.
Download the Lion 4.3.1 XCode DMG file, and mount it so that you can see it from Finder.
Fire up a Terminal (Applications->Utilities->Terminal) - don't worry UNIX-virgins, it's all straightforward
Now enter the following commands into the terminal (note, your password will have to be entered after the first command):
sudo cp -R /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS5.1.sdk /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/
sudo cp -R /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator5.1.sdk /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/
sudo cp -R /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/5.1\ \(9B176\) /Developer/Platforms/iPhoneOS.platform/DeviceSupport/
cd /Developer/Platforms/iPhoneOS.platform/DeviceSupport/
sudo rm -f ./Latest
sudo ln -s ./5.1\ \(9B176\) ./Latest
Now just unmount the dmg in Finder, fire back up XCode, and your 5.1 device will now work with XCode 4.2...