Using the Spatial Data Import Com Add-in, I have had zero success importing ArcView street centerlines. Is their a certain format / structure the street centerlines need to be in before importing?

The MSDN article that goes with the Spatial Data Import sample has not yet been posted, but it may list this type of entity as one that is not supported. The COM Add-In really is just a developer sample that demonstrates how vector and point data from other file formats can be added on top of a MapPoint map - clearly it isn't meant to be a comprehensive ArcView file converter.