"In Luke 16 (where it talks of Lazarus and the rich man) do you believe that there is a "gulf" between the souls in Hades, and the souls that have made the first resurrection?", (Question from Dewayne Short).
The gulf of Hades is an interesting teaching, that has gained some popularity, especially on the internet. I would describe it as being a generally more informed position on the state of the dead, but not quite right. The gulf of Hades assumes two things. First, that people couldn't go to heaven in the Old Testament, and second, that Jesus later freed them and brought them to heaven at his ascension.
The term "gulf of Hades" comes from Luke 16, which describes Lazarus and the rich man as being separated by a impassable gulf, or chasm, "And beside all this, between us and you there is a great gulf fixed: so that they which would pass from hence to you cannot; neither can they pass to us, that would come from thence" (Luke 16.26 KJV bible). On one side of this gulf is the rich man in torment, and on the other side of the gulf is Lazarus, being comforted in the "bosom of Abraham".
The question as it relates to the gulf of Hades, is whether this gulf separates two different sides of Hades, or whether this gulf separates heaven from Hades on a spiritual level. Luke 16 really doesn't tell us one way or another, but only identifies one side of the gulf as Hades, and the other side of the gulf as Abraham's bosom. So the question is whether Abraham's bosom is true heaven, or just a more pleasant subdivision of Hades?
To really understand the gulf of Hades, we need to know whether the saints from the Old Testament had gone to heaven when they died. Some of them apparently did, because Elijah gets taken up to heaven, and doesn't come back, "Behold, there appeared a chariot of fire, and horses of fire, and parted them both asunder; and Elijah went up by a whirlwind into heaven" (2nd Kings 2.11 KJV bible). We also know that Moses appears with Elijah on the Mt. of Transfiguration (Matthew 17.2-3). If the two appear together at the same time with Jesus, then Moses was probably in heaven with Elijah at that time. There is also an Old Testament reference to the redemption of Abraham, "Therefore thus saith the LORD, who redeemed Abraham, concerning the house of Jacob" (Isaiah 29.22 KJV bible). Thus, if the Lord had redeemed Abraham, and he went to heaven, then Abraham's bosom must be a reference to heaven itself, and not a part of Hades.
Under the first covenant, much of what was established by God, including the sacrifices and priesthood, were only place holders. These temporary place holders symbolized, and looked forward to, what would be established in Christ. So the redemption of the Old Testament saints was not at odds with Christ, because every one of them were complicit in the overall plan of Christ. God simply forgave their sins and accepted them, prior to the preordained fulfillment and completeness that we partake of now. This is why Christ, being part of the Godhead, forgave the sins of many before his crucifixion, "But that ye may know that the Son of man hath power on earth to forgive sins, (then saith he to the sick of the palsy,) Arise, take up thy bed, and go unto thine house" (Matthew 9.6 KJV bible).
We also need to consider whether Christ set people free from Hades, and brought them to heaven at his ascension. We know that Christ first descended into Hades as he bore the trangressions of others (Matthew 12.40). We also know that while he was in Hades, he proclaimed good news unto the souls of the dead, "For for this cause was the gospel preached [Greek: Kerusso - to proclaim or herald] also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit" (1st Peter 4.6 KJV bible).
However, we can't assume that this proclamation of good news to the dead was in some way an opportunity to believe upon him, and receive salvation at that time. It most likely pertained to the Resurrection of the Dead, when all of the dead will be freed from Hades, and judged according to their deeds in the flesh (Revelation 20.13). This is why Peter speaks of them being "judged according to men in the flesh". So while Christ did descend into Hades and make a proclamation unto the dead, he didn't free souls from Hades, and bring them into heaven with him.
One verse that is sometimes used to support the gulf of Hades theory is Ephesians 4.8, "Wherefore he saith, When he ascended up on high, he led captivity captive, and gave gifts unto men" (Ephesians 4.8 KJV bible). Unlike some other translations, the King James translates this verse correctly, in that he led "captivity captive". It doesn't say that he led a host captives out of captivity, or any of the other mistranslations that are out there. At his ascension, Christ made captive the captivity of sin and death. In other words, for those who believe upon him, he removes the captivity of sin and death, giving them eternal life.
The gulf of Hades is an interesting theory, that shows a more advanced knowledge of the bible. However, the true meaning of the gulf in Luke 16, is that it represents a spiritual separation between those who are in heaven, and those who are in Hades. Abraham is a father to those who walk by faith (Romans 4), and Abraham's bosom represents true heaven, the dwelling place of God and his angels. Hades and heaven are the two current spiritual, not physical, realms of the dead, and the gulf of Luke 16 is a spiritual barrier that separates the souls in Hades from those in heaven (see also Underground Hell, Space Heaven).