Unfortunately I lost track of how I'd got to the various pages as it's referenced from a few places - in part reflecting that you can get to the dialogue itself from various places, including from CD ripping, file conversion (right-click > send-to) and of course the preferences menu>file converter, so it's probably in those links. I did a search for Nero at one point (after seeing this thread that suggested there was an updated link in at least one of those!) and it came up with 4 results. Sorry that's all a bit vague.
I did download from the free codecs link I quoted, and moved the neroaacenc.exe file into the correct MB directory, but when I tried to convert a file from FLAC to AAC it didn't do anything, just stayed on the convert dialogue. Haven't had time to investigate further as yet, will report back when I do. I'm on MB 3.0.5977 btw. Maybe I just need to restart MB or something. >> Edit: yes, restarted and it's fine now.
Thanks