SRM Development--URGENT

Hi,

I'm new to SRM development. The task I'm currently working on is to filter the tax rate showing drop down in shopping cart (add to cart -> description).

I believe there would be some BAdi that would serve the purpose but i'm not sure: 1- how to locate appropiate BAdi.

2- how to implement/code that. would it be same procedure like in R/3?

3- what would be the testing procedure.

is there any specific IDE for SRM? please let me know how to proceed with that and also refer any helping guide for SRM development.

Regards,

Shabbar