[CentOS] looking for alternative to SME & Clark Connect

Hi all,

I'm looking for a (preferably free) alternative to SME / Clark Connect.

I basically need the following:
- firewall
- nat
- VPN
- bandwidth limiting / monitoring
- email (SMTP / POP3 / IMAP) & groupware
- file & printer sharing
- RAID support
- if possible fail-over / high availability support.

I need to support about 15 - 30 (some part time) students, so I would
like to keep the costs low. If it's free, so much better. SME works
for most of the stuff, but it still runs on CentOS 4, and I'd prefer
to use 5.

Any recommendations?

-- 

Kind Regards
Rudi Ahlers