This article explains how to determine which user initiated a SharePoint event.

Normally, one could use the "Originator" to determine which user started a process. A SharePoint event however, is fired under the "ApplicationPool" account of the SharePoint site, and not the user who initiated the event. Therefore the ‘modified by’ field changes as soon as™ 2003 performs any action on the document.

To obtain the username of the person who initiated the SharePoint event, follow the steps outlined below:
1.  Add a new column in your SharePoint document library by clicking on the "Modify Settings and Columns" link and selecting the "Add a new column" link.
2.  Specify the column name and select "Calculated Value" under the "Default value" option. Set the value to "=Me", as indicated below:
3.  When a document is uploaded into SharePoint, the user’s name will automatically be populated in this new column.
4.  The new column’s value can now be used in the™ 2003 process when using a SharePoint process template wizard, as illustrated below: