Replies to questions:-
1. It should boot from cdrom, take a look around, and see that it's an installed system. It then should give you the option to "upgrade". (If it doesn't just exit and post mortem; no harm done. It should also ask you whether you wish to "preserve" the contents of the other (non-root) filesystems it can see. Say yes to that. No, it shouldn't want to repartition everything in this scenario. Don't select "initial install" option.
2. As a good sysadmin you must know that in IT anything that can go wrong often does go wrong. It is possible (but not likely) that you could be left with a mix-up between versions. If this is a production system then there must be an existing backup strategy; what is it?
What type of filesystem is it? On Solaris 9 I would expect it is ufs?
If so, in the absence of an existing backup method, I would suggest taking a ufsdump of each filesystem to a tape or remote (nfs mounted) disk.
What separate filesystems do you have? Is /usr a separate filesystem?
Post the output of:-
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