Here is a link to the Microsoft KnowledgeBase that gives you several ways to do it. http://support.microsoft.com/default...b;en-us;812718
However, in the past I have been able to reset the number after deleting the records by running Compact and Repair under the Tools menu. I have read that there is a known bug (or 'feature' ) in Access 2002 and 2003 that causes this not to work (MS Article ID 287756).
why do you want to reset the number field. I can understand iof you are shipping a new system and want to let the client see it start from 1 but if its an internally used number does it matter. For a one off the earlier respondants are right. If you want toi leave data in place delete the indexes, realtionships etc then then column, then re-create the column, indexes & relationships. If you want to satrt with null data, then delete all the data, remove the primary key, change the column type to long integer, save , then changed the column type to autonumber