These notes refer to building rssh on Centos 5.3. I do not cover chrooting the user within their restricted shell because I could not get it working satisfactorily. Nor do I cover the reasons why you might want to use a restricted shell.

The steps I followed were:

Get the code
(1) download the source rpm (2.3.2 at time of writing)
(2) install the gpg key
  rpm --import http://www.pizzashack,org/ddmkey.txt
(3) build the source package
  rpmbuild -v --rebuild rssh-2.3.2-1.src.rpm
(4) install the newly built rpm
  rpm -ivh /usr/src/redhat/RPMS/i386/rssh-2.3.2-1.i386.rpm

Configuring rssh (no chroot)
(1) edit the /etc/rssh.conf file and uncomment the #allowsftp line (and/or #allowscp and/or #allowrsync etc) to allow sftp access (and/or scp and/or rsync etc)
(2) create your user (eg for a user John Citizen)
  useradd -m -d /home/jcitizen -s /usr/bin/rssh jcitizen
passwd jcitizen
(3) test the login for jcitizen from another machine
   (a) connect using ssh
   ssh jcitizen@rsshserver.mydomain.com

   you should see output something like:

Last login: Sat Apr 25 11:00:11 2009 from 192.168.0.10

This account is restricted by rssh.
Allowed commands: scp sftp rsync

If you believe this is in error, please contact your system administrator.

Connection to rsshserver.mydomain.com closed.

   (b) connect using sftp
   sftp jcitizen@rsshserver.mydomain.com

   You should now see some output something like:

Connecting to rsshserver.mydomain.com...
jcitizen@rsshserver.mydomain.com's password:
sftp>

(4) Important - note that this type of configuration will apply to all users with the rssh shell. It is also possible to configure rssh on a per user basis.