To install, untar in /usr/share/emacs/20.[0-4]/lisp/, 'mv calendar calendar-blackup', then 'mv calendar-orig calendar' (if you need to). Apply the patch 'patch -p0 < calendar-patch'.
To set the number of months you want displayed at once put '(setq calendar-months X)' in your .emacs file where X is a digit between 1 and 3. new patch patch-0.2 don't forget to rmove the file diary-lib.elc if it exists.