TheLuddite, All,
Thanks for a very helpful thread. After much cursing it seems to be working. One point I would add for the benefit of Mac users is that if you unzip the nightly files with a mac before moving them to the slug you get an ‘Invalid Magic’ error upon attempting to run ipkg.
I got round this by referring to this thread:
http://forums.fireflymediaserver.org/viewtopic.php?t=5164&highlight=magic
and used wget to pull the files directly onto the slug.