Action based on the UDF value of a field

Hi friends,

I am hoping to explain what I am trying to achieve. Hope to find an answer. This is my situation.

1) I was able to create a User Define Field (UDF) in Business Partner (valid values of 1 & 0).

2) Then I was able to create a User Defined Field (UDF) in Purchase Order (valid values of 1 & 0).

Now here is what I am looking for. When I click OK (trying to create a PO) with 1 as the selected value in this UDF, I want to check the value of BP's UDF and continue the PO creation only if BP's UDF is 1.

Can anyone help?

Thanks,

Manoj.