I was able to replace the TouchWiz calendar with the normal Android calendar roughly according to the directions in this thread: forum.xda-developers.com/showthread.php?t=735035
(Sorry for the crappy link, but I can't do proper links yet.)
I've edited mcb00f's directions slightly and repeated and repeated them here:
1.) You must have root to replace the TouchWiz calendar! Use root explorer or ADB to move TouchWizCalendar.apk, TouchWizCalendar.odex, TouchWizCalendarProvider.apk and TouchWizCalendarProvider.odex to somewhere on your SD Card as backups. Reboot.
2.) Go into manage applications. Filter to all. Uninstall com.android.calendar.apk and com.android.provider.calendar.apk. Reboot again.
3.) Download Calendar.apk and CalendarProvider.apk from the thread referenced above and copy them to your SD card. Install both.
4.) If you want, use root explorer to move them from /data/app to /system/app but it's really not necessary. Reboot again, should sync by default but re-enable if you need to.
If you get an error or it doesn't work, it's probably because you didn't reboot one of the three times you need to do so!
Hope that helps!
Edit: Just in case it wasn't clear, the My Calendar calendar and events in it will be deleted along with the TouchWiz calendar app, so if you have anything you want to keep from that calendar, you should back it up accordingly!