In case anyone, like me, was a little confused by the mountains of info in this thread, and elsewhere on this site, suffice to say that the instructions on wiki.cyanogenmod.org/w/Install_CM_for_olympus work well.
It's a little frightening (for a noob, at least!) to read through page after page of forum posts saying "This will only work on version x, otherwise you brick your phone". The posts were accurate when they were written, of course, but things have changed a lot. It was rather difficult to find out whether these instructions would work with a 4.5.145 firmware from AT&T, for example. It turns out that the older instructions might have trouble, but the most recent set (including the link above) are fine.
Thanks to all the developers and forum posters for all the work - as someone new to the whole android world, it's inspiring to see how quickly things are moving, and how well independent coders can work around the roadblocks set up by the likes of AT&T! I'm happily using CM7.2 now, and looking forward to getting onto CM9 and 10 as soon as they're ready!