Little easier than creating a custom class...
Instead why not create a temporary string variable and assign it by your input box. . .
then check the count in a do until loop...
EX.
Dim str As String = InputBox("Name", [Title]:="name", [XPos]:=50, [YPos]:=50)
Do Until str.Count() > 0 And str.Count() < 8
MessageBox.Show("I am sorry but you need to input between 1 and 7 characters")
str = InputBox("Name", [Title]:="name", [XPos]:=50, [YPos]:=50)
Loop