Hi, I just manage to get the add button onto the Calendar. I followed the instructions from here
http://www.tuaw.com/2007/10/11/hack-enable-adding-calendar-events-on-your-ipod-touch
I dont have a Mac so I am doing everything using a pc and my itouch. I downloaded the N54AP.plist file using ibrickr. Then I went to
http://140.124.181.188/~khchung/cgi-bin/plutil.cgi to convert that to a text file.
I used Wordpad to add the 2 lines from the Tuaw site. Be sure it is added under the 'capabilities' section. And reloaded that newly edited text file back to the itouch. Of course, I had to delete the old file 1st using mobilefinder in the itouch itself.
I rebooted the itouch and it worked when I turned it back on. Hope it helps.