Receiving the Spirit

I have been talking with a friend of mine who is in a small group that happens to be dealing with the book of Acts. Reading through this book makes one think about when the Holy Spirit is received. As we were talking and looking at a few specific passages in Acts, we realized that each seemed to say different things about when one receives the Holy Spirit. So, at a few points in our discussion we had to come to the conclusion that we don't know exactly how to interpret these scriptures on their own. However, my continued reading of "Baptism & Fullness" has helped me to see other scriptures that bring light to the ones in Acts.

Through reading and discussion I hope to solidify my belief that there is no time difference between acccepting Christ and receiving the Spirit. While reading through Acts, I saw that there are three places where the Spirit seems to be given at a later time than when one becomes a Christian. This was very confusing to me, because I have always been taught (and believed through scripture) that the Holy Spirit is received as soon as one accepts Christ.

These passages were 1:15-2:4, 8:9-17, & 19:1-7.
The first passage says there were about 120 "brothers" who received the Spirit--this seemed to be the first time that the Holy Spirit was fully given. They did not seem to receive the Spirit as soon as they accepted Christ, however the 3000 that were saved at the end of the chapter received the Spirit at the time of conversion. Why was there a difference?
The second passage seemed to say that Peter and John were the ones who brought the Holy Spirit through their laying on of hands. When the apostles at Jerusalem heard that Samaria had received the word of God, they sent Peter and John. Why? There is no evidence that on other occasions evangelistic work had to be inspected by two apostles. Does it seem that Philip's preaching and baptism were not complete enough for the Holy Spirit to fill these men? In the same chapter Philip preached the gospel to an Ethiopian eunuch and baptized him when he believed. But no apostle was sent to investigate or to lay hands on him. Why was there a difference?
The third passage I noted is confusing because these men are called disciples, yet they "have not even heard that there is a Holy Spirit." Were they Christians before Paul layed hands on them and baptized them? Can someone who has never heard of the Holy Spirit or been baptized in Jesus be a true Christian disciple? I find that hard to believe. They may have been disciples of Apollos or John the Baptist, but not of Jesus.

What do you take from all this? When do we receive the Holy Spirit? Why do these instances seem to contradict? Is there other scripture we can use to help us better understand the receiving of the Holy Spirit?

As a Christian I believe that Scripture is God's word written for our learning. All our traditions, all our opinions and all our experiences must therefore be submitted to the independent and objective test of biblical truth.