WHT Vend & cust

Hello Experts

I am an Issue where My vendor is providing me material supply as well as sub contractore service also. I want to keep a validation that when Bill is for material supply WithHolding Tax pop up should not come But when the same Vendor Bill is for SUB Contractor it should pop up With Holdint Tax Window. How can I do that. Same for Customer also My customer avalis product as well as service also. It is not possible to define diffrent Vendor Becasue there is huge list of vendor and customer. Is there any way I can have validation on this..PLZ guide me in this issue.

Thanks a lot

Regards

Pooja