date/time ValidationExpression

Hi
i have a textbox that takes date/time
my problem here is for invalid date format how to use the RegularExpressionValidator ValidationExpression to show a text in red near my textbox (something like Invalid Date Format)
e.g.
user types in my textbox
[45 Jan 2006] Invalid Date Format
[12 Mar 2008  77:23:20] Invalid Date Format
[29 Feb 2007] Invalid Date Format
[abcdefg] Invalid Date Format
 
i ...