Open source file monitoring for Windows servers?

[itm]

I'm looking for a free or open source utility which will monitor a Windows 2003 server for changes for critical files (e.g. system files, web sites, etc). Can anyone recommend something that'll do this?
It would also be useful (but not essential) if it were able to monitor the health of ASP.Net websites, server CPU and server disk I/O.
TIA for any suggestions

 

[itm]

The Audit tool seems to be designed to audit access by specific users. This requirement is for compliance purposes, and is designed to monitor for unauthorised access (i.e. where the user would be difficult to predict). Is the Audit tool an appropriate way of meeting this sort of compliance requirement?