This problem is addressed in ArcGIS 8.1 Service Pack 1. See Related Information section to download this pack.
If the Attributes dialog is open when the Divide command is used against a network edge, the selection set is not properly cleared. If any attribute of the remnant feature is then modified, ArcMap will crash.
Upon completion of the Divide command, the original feature remains selected; however, when a simple edge feature is split, the original feature is deleted and two new edge features created. If the attributes dialog is open at the time of division, ArcMap holds a reference to the original feature.
Close the Attributes dialog prior to executing the Divide command.