How can I check who last opened a file?

Enable auditing for files and folders via User Manager (Policies - Audit - Audit These Events - File and Object Access). In Windows 2000 use the Group Policy editor and edit the local policy or another GPO (Computer Configuration - Windows Settings - Security Settings - Local Policies - Audit Policy)

Start Explorer

Right click on the files/folders select Properties

Select the Security tab

Click the Advanced button

Select the Audit tab

Click Add

Select 'Everyone'

Click OK

Select the actions to audit such as 'List folder/read data'

Click OK

Click OK to all dialogs