Depending on what Mini you have it would of been shipped with 10.3.7 or 10.4.2, so it does depend on what version disc (as previously said 10.4, 10.4.3, 10.4.8) and you have and what mini you have (early, mid or late 2005).
Also you cant boot off a CD holding 'C' you would have hold option and wait to see if the CD over firewire is recognized.
Yes, have tried that and the only disc it would boot from was Snow Leopard which of course is an intel version and won't work. Have ordered restored discs specifically made for this mac mini...hopefully that will solve the problem.