Is it possible to install Xampp on this server, making it available through the external IP-adress of the server?
yes, but you will have to shift either XAMMP or IIS to a different port. IIS is used by Microsoft's webmanagement protocols for many tasks, so you might cripple your install by urning it off. Why not just usee IIS???
- What do I have to install to be able to work with odbc connections (because that's, in my opinion, the easiest way to reach the database)?
Since XAMMP only really has support for MySQL and SQLite built in. So, other than programmatic methods. ODBC is probably the only way get to your data. You are probably in the wild blue yonder with this mix.
I just have this looming question - if you wanted Apache and SQLbase, why are you on a Samll Business Server? - its a bundle designed to support compeltely different components (I have SBS's myself - I do IIS support and run my own MS servers)
Well, good luck with your project