Further to the discussion at last night's meeting, regarding swapping problems under the Linux 2.4 kernels, I found the following bug report at Red Hat's bugzilla site...
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=60079
There's also a new, open bug report that seems to describe the same thing...
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=61007
... but that one hasn't been dealt with by Red Hat support staff yet.
The solution for now seems to be to upgrade to the 2.4.18 kernel, which has a newer and more aggressive page reclamation algorithm. For now, this means either compiling your own, or using the kernel*-2.4.18-0.13 RPM's from the "skipjack" beta, or the kernel*-2.4.18-0.18 RPM's from rawhide. To use the RPM's, you'll also likely need to upgrade a few other support packages (initscripts, dev, and iptables, for example) from the same distribution.
As of today, there aren't any packages available for supported versions yet. So, you can either go for an unsupported upgrade (beta or otherwise), or wait for the next official Red Hat release.