[CentOS] Low-memory Centos5?

[D Steward]

IMO, CentOS is not a good choice for old hardware with small amounts of
ram, esp since the apps you want to use (Fx2 and OoO) are notorious for
being profligate with ram.

If no-one here can point you to a Redhat-based distro with modest
requirements, you could check out Zenwalk, which uses XFCE. It is a
slackware-based distro and is famous for including only one app for each
task and running like the blazes on old hardware.
It is not a cutdown semi-useable distro like DSl and puppy.