I think I may have figured it out using the bible according to Patrick. Here's my solution
The following is in a OnBeforeChange event handler
Dim dToday As Date = DateTime.Today()
Dim vToday As Date = dToday.AddDays(-90).ToString
Dim idNumber As String = e.Site.text
If (idNumber > DateTime.Today) Then
e.ReturnMessage = "The incoming date can not be greater than today"
e.ReturnStatus = False
ElseIf (idNumber < vToday) Then
e.ReturnMessage = "The incoming date can not be less than 90 days ago"
e.ReturnStatus = False
End If
I'd still like to know how to insert dates programattically though....