Referencing external file with Index/Match functions

I am trying to run a simple Index/Match query in one excel file where it indexes from an external file. Now the file gets renamed every other day. So I want a way to refer to "any" or * file in a particular folder. Here's the query I have right now:

=INDEX('http://....../[ADV_Project_List_09-08-10.xls]Project Mapping Data'!$B$2:$B$128,MATCH(K14,'http://....../[ADV_Project_List_09-08-10.xls]Project Mapping Data'!$W$2:$W$128,0))

Now you can guess that the date is what changes about the filename. The old file gets moved out of the folder so at all times there's only one file in that folder. All I need to do is refer to just that one file somehow and be able to do that without having to change the date in my query every day.

Is there a way I could do something [*.xls] instead of using the complete filename?

Please let me know if this doesn't make sense. Thanks for your help.