In Luke 1:67, was Zechariah filled with the Holy Ghost as the Apostles were in the book of Acts? It is my understanding that the Holy Ghost was sent after the death of Christ.
This answer is from a Pentecostal perspective.
We can see that the Holy Spirit was actually in operation in terms of empowering people for serving God in the Old Testament. The earliest explicit reference to this is in Exodus in regard to the artisan Bezalel:
Then the Lord said to Moses, 2 “See, I have chosen Bezalel son of Uri, the son of Hur, of the tribe of Judah, 3 and I have filled him with the Spirit of God, with wisdom, with understanding, with knowledge and with all kinds of skills— 4 to make artistic designs for work in gold, silver and bronze, 5 to cut and set stones, to work in wood, and to engage in all kinds of crafts. - Exodus 31:1-5 NIV (emphasis added)
It is a common refrain in the book of Judges that "the Spirit of the Lord came upon X" (Othniel, Gideon, Jephthah, Samson) prior to God using them to deliver the Israelites from their enemies, but it is also used elsewhere regarding David and many of the prophets (cf. Judges 3:10; 6:34; 11:29; 14:6; 1 Samuel 16:13; 2 Chronicles 20:14; 24:20; Ezekiel 11:5).
In the New Testament, as well as Zachariah, both John the Baptist and Jesus himself are described as being full of the Holy Spirit prior to the advent of Pentecost. (cf. Luke 1:15; 4:1)
So what was so special about Pentecost? Why did the disciples have to wait for that particular moment to be empowered when God had previously empowered others for his service on many different occasions?
The Apostle Peter clarifies the distinction by describing Pentecost as the fulfillment of Joel's prophecy:
14 Then Peter stood up with the Eleven, raised his voice and addressed the crowd: “Fellow Jews and all of you who live in Jerusalem, let me explain this to you; listen carefully to what I say. 15 These people are not drunk, as you suppose. It’s only nine in the morning! 16 No, this is what was spoken by the prophet Joel:
17 “‘In the last days, God says, I will pour out my Spirit on all people.
Your sons and daughters will prophesy, your young men will see visions, your old men will dream dreams.
18 Even on my servants, both men and women, I will pour out my Spirit in those days, and they will prophesy. - Acts 2:14-18
Prior to this event, God had poured out his Spirit on particular people at particular times for particular tasks. Pentecost marks the start of "the last days" where the Spirit is being poured out "on all people" - ie every 'ordinary' believer in Christ can be full of the Holy Spirit:
37 When the people heard this, they were cut to the heart and said to Peter and the other apostles, “Brothers, what shall we do?”
38 Peter replied, “Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit. 39 The promise is for you and your children and for all who are far off—for all whom the Lord our God will call.” - Acts 2:37-39 (emphasis added)
Elsewhere in scripture, we are taught of the operation of the Holy Spirit within us - to convict of sin, righteousness and judgment; to comfort/edify; to teach/lead us in to all truth; to help us claim Jesus as Lord; to regenerate our hearts; to provide the seal of our adoption into the family of God etc. Some of these operations are actions of the indwelling Holy Spirit and are what is new in the operation of the Holy Spirit under the New Covenant.
The day of Pentecost on the other hand, was particularly about the Holy Spirit coming upon the Church to empower them as witnesses for Christ - the operation of the Holy Spirit in this resepect it was quite similar to the operation of the Holy Spirit under the Old Covenant, the principal difference being not so much in the mode of operation, but in its degree.