Problems with one iMac

[fistro@]

I've problems to boot one iMac grafit G3 400, to instal debian, with the 
Debian 2.2rev3 potato cd, also with de Suse 7.1 cd.None of both run in 
the iMac, but I,ve install in mi iBook both distributions without 
problems, if someone can help me....
Thanks fistro@