Field-level and interfield validations

Interfield validations on the same screen also should be done when the user visits the latter field. Is this possible?

Answer:
The perfect method for validation is the aptly named Validate(), fired whenever a user changes a value in a field and leaves the field.

Regarding interfield validation, your description is slightly off base. In a graphical application, you have no way of controlling which field is 'last' to be visited. The way I would implement this is to declare a user-defined method and call the method from the Validate() method for all of the the fields that participate in the validation.