you have many options.
one. to reinstall.
put cd in drive, then type boot cdrom
it will start the install in a few minutes.
It will ask you many questions, one being do you want it networked..answer NO.
you can customize the slices on the disk, I suggest you do that.
A slice is as follows.
slice 0 is root
slice 2 is the whole disk
slice 3 is swap
etc.
by cutomizing ,you can allocate more space to
/usr,/var/, or /export/home/username
I use my U5 to connect to work via vpn, It works great!!
two..
if you don't want to reinstall then I believe you can then " sys-unconfig" the machine.
after typing sys-unconfig..power the machine off with "power-off" from OK prompt, then power it back on.
once it starts coming up it will ask you a bunch of questions, one is if you want it networked.
if you don't reinstall then the person prior was correct, you must fsck the drive.
it looks like your root drive has incosistencies.
the easiest way to do it is like this
fsck -y /dev/rdsk/c0t0d0s0
hope this helps
Dave