I'm not certain what version of Visual Studio you're using - I'm still using 2003 however we have purchased and installed 2008 and I am preparing to start using it in the next week or two..
however in 2003 in your toolbox you have the required field validator you can use - you set the validator to validate the date textbox or whatever you want and in the operator field of the properties you chose greater than or greater than equal if you want them to be able to enter todays date.
you can then insert a validation summary from the toolbox and in error message of your validator you can list the message you want to place in that summary area. So you can say "Date can not be prior to today" and it will tell them what's wrong. You can even insert a second validator and make it required so it will make sure it's also not blank and so on.
you can mess with settings like make the color red etc.
Then in your code you can put in a valid fields check - an example I've used for one of mine is here
Private Sub ValidFields()
Dim strError As String = "Validating Request."
Try
cpvRequestedDueDate.ValueToCompare = DateTime.Now.Today.ToShortDateString
rfvReqUser.Validate()
rfvTitle.Validate()
rfvDescription.Validate()
rfvPriority.Validate()
cpvRequestedDueDate.Validate()
cpvRequestedDueDate2.Validate()
rqvDueDate.Validate()
Catch ex As SqlException
PageUtil.ShortProcessErrors(ex, Session, Me, strError)
PageUtil.ShowError(Page, strError)
Catch ex As Exception
PageUtil.ShortProcessErrors(ex, Session, Me, strError)
PageUtil.ShowError(Page, strError)
Finally
End Try
End Sub
in the above example - rqvDueDate is one validator that was inserted to validate due date. That name was set in the id field of the properties.
Unsolved 
