The date only part:
           Convert(DateTime,Convert(VarChar(11),DateTimeField))

If you have to do this quite often, consider creating your own function that
is the equivalent of DateValue().

-- Function to remove the time value from a date and time
Create Function DateValue
(@DateAndTime datetime)
Returns DateTime
AS
BEGIN
Return Convert( DateTime,Convert(VarChar(11), @DateAndTime) )
END

You can then use the function in your SQL like
 dbo.DateValue(DateAndTimeField)