Getting the SAP Business One Developer Tools

Hi Guys,

Can someone point me in the right direction?

I am a software developer and have a customer who is about to buy SAP Business One, they may need some customisation and have asked if I'd be able to do it.

I wonder if anyone could let me know how to get started, do i need to become a SAP Partner? or just get my customer to buy the developer tools as a module?

Mike