Greetings Hovi,
Below are links with specific information on each distribution, but to summarize, CentOS-2 is a clone based on RHEL2, CentOS-3 is a clone based on RHEL3, and cAos-1 is based on RHL7.x, but is not a clone, it is a new RPM based, yum updating linux distribution.
The CentOS versions are aimed at servers if you think RHEL is aimed at servers, but cAos will work on servers just fine.
The available software packages for CentOS version can be found linked on their respective pages (links below).
I do not have information on the Dell PowerEdge line, or the 2300 specifically, but if RHEL installs on it (and I imagine it would), CentOS versions should too. I imagine cAos would too, but you'll have to tell me if that is just my imagination. I have posed the question on the cAos IRC forum (#cAos on irc.freenode.net), and if I receive an answer I will post it here.
Caos:
http://www.caosity.org/index.php?opt...=page&SubMenu=
CentOS-2:
http://www.caosity.org/index.php?opt...=page&SubMenu=
CentOS-3:
http://www.caosity.org/index.php?opt...=page&SubMenu=
Troy