There has been more than one Time War. The Time War featured in a number of novels published in the early 2000s by BBC Books did indeed involve the Eighth Doctor. The Last Great Time War, as referenced in the 2005-present revival series, has been confirmed by Russell T Davies as being a separate conflict (think World War I, World War II). "The Night of the Doctor" revealed that the Eighth Doctor was involved in the Last Great Time War only to the extent of helping its victims where he could. That story also revealed that he regenerated into the "War Doctor". The "War Doctor", not the Eighth Doctor, fought in -- and ended -- the Last Great Time War, as shown in "The Day of the Doctor".