Hi,
Upon reading your post, I just thought "it seems stupid to implement :next and not :previous". Why on earth would I do that? Then I've seen: I implemented :next and :Next (for :previous), thinking that was it, and I didn't know about the commands you have suggested. I've taken note of your suggestions though to implement them soon.
On the other hand, :n and :N, like :bn and :bp, actually walk along the list of files that ViEmu has seen (you can see it with :ls). There is a bug now, in that a buffer is removed from this list when closing it with ":bd", but not when closing it with ":q" or with VS's own commands, but this will be fixed soon. If it seemed to you that :n opened the next file in the solution explorer, it's likely because that file had been open recently.
On the other hand, VS's tabs do not support any kind of extensibility interface. There is no access to them, and the only way you can interact with them is using "Window.NextTab" and "Windows.PreviousTab" -- there are also ".MoveToNextTabGroup" and ".MoveToPreviousTabGroup", but that is about all. Thus, I have to resort to ViEmu's internal file list for these operations. Unlike Word's, VS's extensibility is generally pretty comprehensive, but there are some limitations about what can be done.
Regards,
-- Jon