As I recall the Cistron sources still build on centos-4, but freeRadius is the future, and also builds on centos. I do not know the patches you are thinking of to the pppd; I assume we are talking about a multiport serial card to be worth the effort? More details are needed, but it should all still work just as it did on RHL7.
Yes, it's a rocketmodem/port multi card.
I am probably the last subscriber still on the RH PPP list,
I joined just to look at the archives. Not much traffic there ;)
and at one time published a patch for an option back in the RHL days which fixed a broken RH option in the PPPD package for Windows unit support. Ask with specific questions if you hit a hard spot -- I still have two dialup ISP clients running local modem pools.
For the record I ended up downloading the source for ppp 2.4.4 which now includes a radius plugin. So at least there is no patching required (the patch is still out there, but I think it's for 2.4.1). It would be nice to have someone maintain an RPM in a reputable repo for it, but I really wonder how much need there is for this particular configuration. It would be interesting to find out what if anything others are doing to provide dialin services with CentOS. With broadband getting cheaper and hot-spots becoming more accessible we find far less need, but there are always those situations...
alex