> 1. Single signon across servers

I Recommend:
Novell eDirectory on Linux
http://www.novell.com/products/edirectory/

Novell has been in the directory business a long time and I think they have the
best LDAP compliant directory service available. And it runs on many different
platforms (Linux) so you don't need a Netware server.

Also, check out:
NSS_LDAP and PAM_LDAP
http://www.padl.com/Contents/OpenSourceSoftware.html

> 2. tape back-up - automated I assume

There are all kinds of backup solutions available for Linux. I would check to
see what solutions they have in place now on their other servers and see if you
can just add an agent to the Linux servers. I know Backup Exec has agents you
can install on most Linux servers. You then schedule a backup from a centralized
backup server and it communicates with the agent which then uploads the files.
http://www.veritas.com/

For a Linux only solution I hear Bru is very popular. However, I have not used
it myself.
http://www.tolisgroup.com/

> 3. system monitoring - performance, capacity, security

There are many ways to skin this cat. Are you talking about a SNMP based
solution here?

Read up on Net-SNMP (previously known as ucd-snmp)
http://net-snmp.sourceforge.net/

Also, look into Webmin. It's mainly for administration and configuration, but
with some third-party modules you can use it to monitor just about everything.
http://www.webmin.com/