Your friend is partly right. Both the New and the Old Testament describe a place where the soul goes after life which is a sort of in-between existence before the final resurrection, judgment and eternity in either heaven or hell. The New Testament labels this waiting place as Hades (Matthew 16:18, Revelation 1:18, and most relevant Revelation 20:13). There is evidence that Hades is divided into a "good" place called Paradise in the Bible and a bad place called Hades. We should be careful not to over-interpret a parable, but this is indicated in the Parable of the rich man and Lazarus (Luke 16).
The Old Testament also suggests a waiting place. Here we find a place called Sheol and one called Abaddon. These terms are found throughout the Psalms. Some versions translate Sheol as "the grave." We can tentatively identify Sheol as Paradise and Abaddon as Hades. However, the Old Testament gives us relatively little to go on, so we ought to be cautious about making this identification. It may be a bit frustrating, but there are things which the Bible in general, and especially the Old Testament leaves somewhat enigmatic. Its description of the waiting place is definitely in this category.
Hades is not the eternal afterlife. Revelation 20 describes Hades giving up its souls at Judgment Day. These souls are then judged and go to eternity with or separated from God–heaven or hell. The Old Testament says relatively little about the final resurrection, heaven and hell. This fact will be surprising to many Christians. Daniel chapter twelve has the clearest description of the final resurrection in the Old Testament.
So your friend is partly correct, but he/she makes a common error of biblical interpretation. We cannot "disprove" one Bible teaching by pointing out another. The existence of Sheol does not preclude the existence of heaven or hell. Let me suggest a DVD series by Douglas Jacoby titled "What Happens When We Die?" This is a very thorough treatment of both the Old and New Testament teaching about the afterlife, as well as a study of Jewish ideas. It is available at www.ipibooks.com.
John Oakes, PhD