Steps to creating a new field in an Attribute table within ARC 9.1 are given.
Steps to Add a New Field to the Attribute Table of a Shapefile in ArcGIS:
1. In the Data View of Arcmap, add the Shapefile you want to add the new field (also known simply as a Column in a table) to so that it appears in the Layers window on the left.
2. Right click on the Shapefile in the Layers window, then click on "Open Attribute Table".
3. Click on Options -> Add Field.
4. Give the Field a name. Make it brief and to the point, try to make it so you will recognize what it stands for. No spaces allowed in the name and do not start the field name with a number.
Attribute table within ARC 9.1 formation is demonstrated.