It appears that Nook does not support .cbr or .cbz files. Calibre will convert a .cbr file to epub, which can be read on a Nook. BUT, it seems to convert only to black and white. Well, what would you expect, books being in b&w after all?
Converting to RAR and ZIP, respectively, then unpacking the jpegs would let you read the comic using the viewer, I think. It's just a bit time consuming. I use a basic, cheapo Nook reader for books but for comics, you cannot beat a Samsung android device using Perfect Viewer. PV now has a pdf tweak which greatly enhances the ease of viewing pdf files.
Sorry I can't be of more help.