newB: can't format date UK to US [working]

I am still new to VB and .NET
I have searched this forum and tried lots of code and nothing works. Here is what I want to do and what I have:

user enters date into textbox1.Text as 28/4/2003
my code should format it to 4/28/2003 and test if isDate

'Check if it is a valid date.
Dim dtDate As Date = textbox1.Text
Dim strDue As String
strDue = Format(dtDate, "MM/dd/yyyy") 'this should format

If IsDate(strDue) = False Then
lblMessage.Text = "Please enter valid due date."
lblMessage.Visible() = True
txtDueDate.Text = ""
Label1.Text = strDue
Label1.Visible = True
Exit Sub
End If

The code above returns an error:
Cast from string "28/4/2003" to type 'Date' is not valid.

If I make dtDate As String then
strDue = Format(dtDate, "MM/dd/yyyy")
returns MM/dd/yyyy in Label1.Text
I used the Label1 to see what the return value of Format is.

Please help me understand what is happening!

ms-help://MS.VSCC/MS.MSDNVS/vblr7/html/vadatDate.htm

"Date values must be enclosed within number signs (#) and be in the format m/d/yyyy, for example #5/31/1993#. If you convert a Date value to the String type, the date is rendered according to the short date format recognized by your computer, and the time is rendered according to the time format (either 12-hour or 24-hour) in effect on your computer."

You may also want to look at DateTime.Parse:

ms-help://MS.VSCC/MS.MSDNVS/cpref/html/frlrfSystemDateTimeClassParseTopic.htm

Thanks SL the DateTime.parse works to swap dd/MM to MM/dd.
However, why does a wrong date like #$/4/2003 get converted to 4/1/2003 after the parse? I put a Try and Catch in but it does not catch all non number chacters as shown above. Any clue?
Here is my code:

Dim strMyDateTimeUK As String
Dim myDateTimeUS As Date
strMyDateTimeUK = txtDateUS.Text 'from textbox
Try
myDateTimeUS = System.DateTime.Parse( _
strMyDateTimeUK, _
dtFormat, _
System.Globalization. _
DateTimeStyles.AllowWhiteSpaces)
Catch ThisExcep As System.ArgumentException
' At least one argument has an invalid value.
lblMessage.Text = "ArgumentException."
Exit Sub
Catch ThisExcep As ArgumentOutOfRangeException
' The result is later than December 31, 9999.
lblMessage.Text = "ArgumentOutOfRange."
Exit Sub
Catch ThisExcep As InvalidCastException
' GivenDate cannot be interpreted As a date/time.
lblMessage.Text = "InvalidCastException."
Exit Sub
Catch ThisExcep As Exception
' An unforeseen exception has occurred.
lblMessage.Text = "Exception."
Exit Sub
Finally
lblMessage.Visible() = True
End Try

I dunno, I see exactly what you mean - no exception is generated DateTime.Parse for a great many non-numeric characters (~, !, pretty much any non-alpha I tried). You might also look at ParseExact but ParseExact seems extremely picky (as the name would suggest).

For now this seems to meet my needs.

myDateTimeUS = System.DateTime.ParseExact( _
strMyDateTimeUK, _
"d", _
dtFormat, _
System.Globalization. _
DateTimeStyles.AllowWhiteSpaces)

'FYI dtFormat is created using:
'Dim dtFormat As New System.Globalization.CultureInfo("en-GB", True)

Thanks for the help!