Snowbot - Try uploading an un-hacked version of functions_calendar.php into your forum/includes folder and see if that makes a difference. That will add the arrows back and make the calendar slightly wider than the rest of the blocks, but you should try that to test and see if it's a problem with the file, or if you are somehow missing the calendar phrases.
The Quibbler - To add more custom blocks, just copy the content from one of the other custom blocks and then paste it into your index template where you would like it to appear.