Auto Update File.lastModifed

I have a list of files that appear on my web page and I would like the update tag to be automatically updated based on the date of the file. As it stands I have to manually enter in the correct date each time the files are changed. Any ideas on how to do this?


<li><a href="literature/Phone List.xls" target="_blank" id="abc">Company Phone List</a><br>Updated July 2007 &nbsp;<img src='images/file_icon.gif' alt='' width='9' height='12' border='0' /></li>

<li><a href="literature/Name and Extensions List.xls" target="_blank" id="abc">Office Names & Extensions</a><br>Updated July 2007 &nbsp;<img src='images/file_icon.gif' alt='' width='9' height='12' border='0' /></li>

Note:
1. I have tried the document.lastModified method but it only gives me the date and time of the html page update not the files. My intent is that indiviuals can ftp there files into specific directories that they have access to and the update tag will automaticlly read the file date and show it on the screen. On each page there are multiple files / documents with differnet dates.

2. I have ASP.net setup on the server so I can do it in ASP if someone knows what code to use...

Thanks,
Brad

Thanks in advance