what kind of software tools do you use to build highly secure payment systems?

Answer 1

You need a merchant's account. This requires permission from one or more banks to be able to set up the account. It is not something you can do yourself. You need to use one of the merchant account services. For a small fee they will set everything up and send you the code to make it work. Check with your hosting service as they may already have merchant accounts available. If not, do a Google for "merchant accounts".

Answer 2

If your talking about over a web-broswer based system, then you should probably look into SSL. Try googling about it, there is a lot of free tutorials out there.