Cannot boot in old MACOS ->help<-


Hi ,
i've installed on my disk (HFS) not + macosx , everuthing works fine , but when i try to reboot in classic mode my imac does not recognize my startup disk, i gotta reinstall macosx to login and see the other partition.
Disk utility if i log on as root , tell me that cannot inizialize start up disk.
is this problem appearing 'cos i have my disk formetted in HFS?
how can i resolve the problem?
anyone ca help me?

I have

I have imac rev.B - 96mb ram disk 4Gb (500mb macos 8.6)
(500mb macos 9.04) 1 Gb for macosx and the rest free ( hfs partition)