Is the Spirit in me?

A little frustrated today, as usual when I don't understand something...

A while ago our pastor preached a series on the Spirit-filled Christian; he said many good things, one of which was that we inherit the Spirit of God and His power the moment we accept Christ into our hearts. This is the "baptism of the Spirit". We do not need to beg for it, or try to "work up to" it, He's already there, and we need only to walk in Him constantly to enjoy the full power of God in us. When we're moving away from God in any aspect of our lives, we are still His children, but we are spiritually weak because we are refusing to tap into the great wealth of strength and comfort given to us through the Spirit.

But if we are baptized in the Spirit when we take up Christ's name in our hearts, what is the meaning of Acts 8:15-17: "They [the apostles] sent off for Peter and John, who went down there [Samaria] and prayed for the converts, asking that they might receive the Holy Spirit. For until then the Spirit had not come upon any of them. They had been baptized into the Name of the Lord Jesus, that and nothing more. So Peter and John laid their hands on them and they received the Holy Spirit."

Is it possible, then, to be a Christian, to accept Christ as Savior, and still be without the Spirit? This was not a case of ignorance on the part of these Samarian converts; they had "accepted the word of God" (verse 14) and "had been baptized into the name of the Lord Jesus".

And in Acts 10:44-48, there is an opposite situation; the Holy Spirit is "poured out even on Gentiles", all gathered in Cornelius's house, before any had been baptized in Christ's name. Verse 47-48 "Then Peter spoke: 'Is anyone prepared to withold the water for baptism from these persons, who have received the Holy Spirit just as we did ourselves?' Then he ordered them to be baptised in the name of Jesus Christ."

I've read that receivers of Holy Spirit speak in tongues and praise God with a vigor that lead many to say they were drunk, or insane, etc.
Acts 10:46 "...for they could hear them speaking in tongues of ecstasy and acclaiming the greatness of God."

Acts 2:4, 5-13 "And they were all filled with the Holy Spirit and began to talk in other tongues, as the Spirit gave them power of utterance. ...And at this sound the crowd gathered, all bewildered because each one heard his own language spoken. ...And they were all amazed and perplexed, saying to one another, 'What can this mean?' Others said contemptuously, 'They have been drinking!'"

1 Samuel 10:10-11 "As Saul turned to leave Samuel, God gave him a new heart. On that same day all these signs happened. When they reached the Hill there was a company of prophets coming to meet him, and the spirit of God suddenly took possession of him, so that he too was filled with prophetic rapture."

David dances before the Ark of the Covenant. People heal and prophesy. Dead are raised. The Church is established. God does great works through His Spirit, and it is His delight to use men and women as vessels of His word and power.

Is there a reason for me to wonder if I, too, "partake of the Spirit", or is this a groundless worry? Have I been baptized with water but not the Spirit? I sing praises, but if I sing in power, it seems that my own emotion is showing through, not God's. I am not charismatic, nor do I think that every Christian must prophecy or speak in tongues upon receiving God's Spirit. But perhaps I do not understand at all what it means to be given Holy Spirit!

I am hoping there is a wise soul out there who can explain some of this to me.