Excel as frontend an XML as backend database? Multiuser capable?

[Bronzato]

Hello everybody,

I'm faced with a problem that I cannot find a solution that suits me. I must start soon a new project that will use Excel 2007 as the user interface. This application must manipulate Excel data (reading, modifying, deleting). For technical constraints imposed by the client, I cannot use SQL databases like SQL SERVER nor ORACLE nor ACCESS, ... Eventually XML files do the trick since it does not handle large amounts of data but the problem is that this application should be multi-user (4 or 5 people). I think XML files (flat files) do not work in multi user environment, isn't? It will certainly happen that several users try to access the same data (tables) at the same time and here I do not think that with the XML I can get out easily.
One of you have an idea to submit to me? I searched a lot without success.

So the constraints are:
- Frontend must be Microsoft Excel 2007
- No DB like SQL Server, Oracle, Access
- Multi User (4 or 5 people)
- Not much data to handle (a few hundred records on a few tables)
- No referential integrity to manage

Thank you in advance for your help!