Thanks for your suggestion, I'm surprised that it's not working!
I finally find out that the partition that I was using was not correct , we should use /sbin/pdisk.
i've tried then: mount -t ufs -o ufstype=44bsd /dev/hda5 /data/ and also with all the other options for '-t ufs' without success

I'm trying to do this on a PowerBookG4
any other hints ??
thanks in advance