iPhone SDK installation on 10.5.2 Leopard
Getting the FINAL SDK to run on a 10.5.2 Leopard box.
1) Install the Iphone_SDK_Final DMG file. It won't let you install the Iphone parts; no worries.
2) Open the Packages folder on the DMG and install all the packages labeled IPHONE and "DeveloperDiskImage".
3) These packages will install into /Platforms, but we need them in /Developer/Platforms. Use Finder, Terminal, whatever, to move these files over.
4) You should at least have a working Iphone Simulator. You'll be able to write code and run it on your PC.
Source : http://www.insanelymac.com