At this time, I'm using nagios 1.2 and have no desire to move to a newer version, since they are still in beta. I've installed and configured the beta's just to help answer many of the questions posted here, but it's simply not worth the effort.
I've installed nagios 1.2 using the documentation dozens of times, and each time, I find the documentation to be complete and not missing a thing.
There is no reason, if you have any linux ability at all, that you can't install nagios 1.2 from source. It does mean, that you have to read and follow the docs though, there is no shortcuts. I still read the docs, and follow the step-by-step procedure's. Good luck.