Im not pretty sure what are you exactly doing, but I think you are not taking the right direction in this one.

However, here are my responses to your questions.

1) You can declare the object to be a IComparable

Code:
Dim obj_Data As IComparable
This obj_Data will only accept instances of objects that have IComparable

2) When you want to check if an object has the IComparable interface you do this boolean expression:

Code:
If TypeOf obj_Data Is IComparable Then
Of course you can erase the IF-THEN.