Use bora when you can (i.e. if there is a bora, and if that repo contains the app you want), and mistral if you have no bora alternative. The mistral distro is for OS2006 (770), bora is for OS2007 (N800).

'components' is the name of a subdirectory in the repository. The reason for having this stems from Debian, where you would typically have 'main', 'contrib', 'non-free', and you could select all (with 3 different entries in the program catalogue list), or a subset (e.g. avoiding the non-free one if you don't want apps with a non-free license). So, 'user' is simply the name of the single subdirectory and the choice of name is pretty much arbitrary. As you have noticed, sometimes it's 'main' or something else.