tar

sysinst use pax to open and write the tar.gz format files. That looks nice, but I have not used frequently, so I will show you the example with tar first,

cd /mnt
tar zxpf $MOUNT/binary/sets/base.tgz 

cd /mnt
for i in $MOUNT/binary/sets/*.tgz 
  do echo $i
  tar zxpf $i
  done

pax

cd /mnt
for i in $MOUNT/binary/sets/*.tgz 
  do echo $i
  pax -zrpe -f $i
  done

replace kernel

For iBook and PowerBook G3 Pismo users, you need to replace the kernel with ADB patch applied. See also versions page.
Precompiled kernel are listed below.
Copy one of those file onto /mnt, gunzip, and rename or (hard)link to /mnt/netbsd.

cd /mnt
mv netbsd netbsd-1.5S
cp $SOMEWHERE/netbsd-1.5V-insecure.gz .
gunzip netbsd-1.5V-insecure.gz 
ln netbsd-1.5V-insecure netbsd