Web Dynpro Java code changes

Hi,

I need to put some validations in web dynpro java page which is "employee address page". I checked the BADI's but no badi exists which serve my purpsoe.

Now I want to make the code change in web dynpro java. Pls answer the followng questions.

1- I have installed NWDS on my local machine. Do i need to install NWDI also?

2- How to import and export the required page and from where?

3- How to modify the standard code, I mean in ECC we have enhancement and modification concept.

Thanks,