Sorry a little late then never... But seeing how support in this forum is PITIFUL, this can hopefully help someone else who may come across this issue in the future.
When you create your column in SQL monitor or PHPAdmin, etc., just set the field type to TIMESTAMP, and the length should be for however much detail you want in the timestamp. For instance, a length of 14 will give you YYYYMMDDhhmmss, whereas a length of 6 gives you YYMMDD.
Once you have the column set, just go into Internal Table Manager in admin.php, and select that column to edit from the drop down listbox. Once you switched to the column, change "Field present in the insert/update form?" to "N", so that the user can't tamper with it when editing the fields. If you need to hide the column for use in another PHP script, you can change all of the visibility/editing values to No.
That's it...
