I have written code (VB / C# in ASP.NET) to integrate an app with the paypal api. do you mean the configuration on the paypal api side (you are a client wanting to use the api) like this (this is how easywebstore uses the paypal api to integrate express checkout) or are you trying to write an app that uses the api?
Could you give a little more info and I will try and help with this.
It's really really easy.. I tried this when I was back in South Africa, but it was a fruitless event since PAYPAL doesn't support any bank accounts in South Africa..!! Wonder y..?