Hi,
I've looked at your requirement and your screen mockup - I can see what you're trying to achieve and in principle, it all makes sense.
The problem may be in how large the XML files are and how many you expect to get built up. If we're using FTP hosting, then your problem is that to create the data grid and enable the filtering, a user would have to FTP down all the files, so they can be read locally and filtered - which could be problematic if the number of files grows large.
Another solution might be to upload the files to a web server with a database (SQL server or MySQL - the latter is much cheaper!) and a web service front end that can process the data (ASP.net or PHP - again, the latter is cheaper to host, although ASP.net can be arguably more secure in the long term). That way, when a user uploads a file, the server parses it, stores all it's data in a db, and when users want to list or filter, this can be done via web services as well, hugely cutting down on web traffic and preventing lots of unnecessary downloads and performance problems.
It all depends on the nature of the XML file (could I see a sample perhaps?) and how many you expect to build up in the online library? I have done this sort of thing many times before though (been developing web services and software, as well as windows apps, FTP apps etc for over 13 years now) so I can work with you to come up with the right solution.
Let me know if you'd like to discuss further,
Regards
Chris
(UK based)