If you mean from a network file server, as long as you're
using the same authentication tokens (passwords), you should
be able to just mount it.

As for old kfs partitions, as long as you have not 
established a new-style Plan 9 partition, your old
partition table will be used when creating the
contents of /dev/sdXX: just use kfs on /dev/sdXX/fs
as normal.

If you're on a disk that you've used to install a
new Plan 9 partition but left your old partitions
there, you can add the partitions by hand by echoing control
strings into /dev/sdXX/ctl -- see sd(3) for more.

Russ