To reproduce/debug an issue exclusive to OS X 10.5, i was trying install Leopard on my Mac Mini (model "macmini3,1", came with Snow Leopard).  
However, when trying to boot from a Leopard install medium (tried both from DVD and USB stick) the machine just hangs:

 * when manually choosing the boot medium: hangs with the boot medium selection screen still displayed 
 * when running the install app from Snow Leopard and letting it restart the machine: hangs with the bright grayish screen and no logo or progress indicator

Does anyone happen to know what could cause this / how to work around it?  

Or could my models hardware be too new for 10.5? Although a web search suggests there were/are macmini3,1s with 10.5 running. Also, [this question and it's resource][1] suggest it should be working.


  [1]: https://apple.stackexchange.com/questions/4400/what-version-of-mac-mini-supports-leopard-10-5-8?rq=1