I created the following folder structure on my cf card : /mnt/cf/oz/feed
This sounds to me like you've created a /mnt/cf on your card? If so you need to remove it and just make an /oz/feed directory on your CF-card to match the ipkg.cong file entry you've made.
In it I have installed the following files from the internet feed:
Packages.filelist
Packages.gz
Packages.txt
orinoco-modules
orinoco-modules-cs
Remove the .txt extension from your Packages file and you should be OK.
Change Packages.txt > Packages
Make sure you are using the Packages file from the feed you've copied the orinoco-modules and orinoco-modules-cs from?
Alternately you could do a search for how to build your own Package file. (there's a script somewhere?)
Greg