This set of posts comes from Pastor Mark Driscoll and his wife Grace. The sermon series The Peasant Princess brought up dozens of questions that they felt they should respond to. The result is this blog series: Christian Sex: Frank Answers to Honest Questions.
Answer: The repeated refrain of the Song of Songs is to not awaken love before its time. Therefore, the issue is not where is the line, but when is the time. The Bible knows nothing of sexual contact of any sort or kind before marriage, as sexual pleasure is reserved for the right person, at the right time, in the right way-which is all in the context of heterosexual covenantal marriage. The NIV translation of Ephesians 5:3 says, But among you there must not be even a hint of sexual immorality, or of any kind of impurity, or of greed, because these are improper for God's holy people.
In 1 Corinthians 7:1 Paul tells single men that they should not touch any woman in any sexual manner. Also, in 1 Timothy 5:1-2, men are encouraged to treat young women as sisters. Thus, since brothers and sisters can and do talk, serve together, enjoy one another's company, etc., there are acceptable non-sexual ways for single Christians to build their relationship in pursuit of marriage. Lastly, in asking how far one can go, there is sin in the heart because the motive is to get as close to sin as possible rather than getting as close to Jesus as possible. The issue is not where is the line, but rather where is your heart and when is the time. That time is marriage.