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.