When I install additional software in my solaris9.0, the error-- do not have enough space occured. I think I must replaning my hard disk to increase the space for /opt. But I do not know if I can re-fdisk the hard
disk in Solaris enviroment? Can you give me some ideas?

Fdisk will kill all data that lives on the particular slice. You need to increase the disk slice of /opt which means you need some kind of partition resizing program. For linux you can use a program called 'parted' to do the job. Not sure if this will support UFS filesystems though. I heard that you can use a program called 'growfs' which is native to solaris. I have never done it before so I can't help you. But if try and you successfully did it, please post how you did as I would like to know how too as well .

-twantrd

The sum of all slices cannot exceed the size of the Solaris partition.
If you want to increase /opt size, that must be by decreasing the size of another slice, usually /export.
You can do it by first doing a backup of /opt and /export to a secure location (and probably also all other sices to be sure), then you can use prtvtoc and fmthard to get and set the slice partitioning you want.
Growfs is not an option, as it works only in conjuction with Solaris Volume Manager metadevices.
By the way, all this will be extremely simplified when ZFS will be made available.