Datetime values are stored as the number of seconds since January 4, 1904 00:00:00 (midnight).
Date values are also stored as the number of seconds since midnight, January 4, 1904 to midnight on the date in question.
Since both values are stored as seconds, you just need to subtract the time of day portion from a datetime value to get the date value.
//today() returns the current date and time
datetime=today();
//subtract the time portion of datetime
date=datetime - time of day(datetime);
//show datetime and date as seconds and then format date to see the date
show(datetime, date, format(date, "mm/dd/yy"));
This can also be done in the formula editor to create a new column with the date. The easiest way is to right click at the top of the datetime column and choose New Formula->Date Time->Date.
-Jeff