Easiest way is to see what it returns for a date you know.
Dim dtmTestDate As Date
Dim strDate As String
dtmTestDate = DateSerial(2006, 1, 2)
strDate = dtmTestDate
Now examine strDate: is it 2006-01-02, or 1/2/06 or 2/1/2006 or ....
For a more formal approach, see what Randy Birch has at
http://vbnet.mvps.org/code/locale/localedates.htm
Obligatory warning: Randy's site is aimed at VB programmers. There are
significant differences between forms in VB and in Access, so sometimes his
examples don't port directly into Access. In this particular example, Access
will not let you set a control's Text property unless the control has focus,
so all of his assignment statements will fail if you simply copy his code.
To get around this, take off the .Text in the assignment statements.