The key to rightly understanding the book of Acts is found by knowing the "intent" and "method" and "history" of that book. In short, the book of Acts is the record of how the infant New Testament church came to be and then its progressive development from infancy to maturity. Racial prejudices had to be overcome by the Jews and the first 10 chapters were given to us to show how God brought the intended universality of salvation and the people of God to reality. Thus there are many things which are temporal and unique which were never intended to be perpetual nor paradigmatic and thus expected to be the "norm" for the mature church through its existence on earth.
I have attached a short section from a book written by Frederick Dale Bruner, A Theology of the Holy Spirit, who goes into more detail concerning this particular portion of Scripture; Acts 8:15-17. I hope you will find it instructive. I formatted it in ".pdf" format so everyone should be able to read it, assuming they have Adobe Acrobat Reader installed. <img src="/forum/images/graemlins/grin.gif" alt="" /> If someone is unable to open the document, you may PM or e-mail me and request this document in another format. I'll do my best to fulfill those requests.