3 tier app, data access layer, business logic layer

Question

hi friends,
I want to develop 3 tier app but I still confused how to implement it

1. In data access layer, could I return datareader? it's the better approach? some people tell it is not good way, you better used arrayList.

2. I have one method with 3 transaction inside (insert, update, delete)
I make this in business layer, so that the OleDBConnection (open and close), OleDbTransaction placed in business layer and I pass this as parameter to data access layer, is that good way?

3. if anyone have the good tutorial especially in C#, please tell me.

Thanks