Ill try to answer one by one.
Q: would there still be any use for my program if i use XML?
A:
Well, it depends on why you would like to use XML in the first place.
If you would like to create web pages that seperate content from UI (-its good to do so , for more detail search for MVC-), of course it would be good to use XML and then XSLT to convert them to HTML.
Q: can these 2 be used together?
A:
Well, it depends on the database you are using.
There are native XML databases and there are Relational Databases. Native XML databases (e.g. EXIST or Tamino) stored data as XML files. Relational database (e.g. SQL server, Oracle) stored data as tables.
Both of the database types still can accept XML, however if we use the former one (native xml database), it would be easier to store. It is still possible though to use xml together with relational databases. One can still actually traverse the XMLDocument object or XPathNavigator object and actually extract the data to store in the database, it would be quite slow though. Anyway, usually only a small part of the xml would be stored in database.
However, Ive read that some relational database have ways too to store xml directly at a predefined format or even better, but I cant comment on those.
Hope the info is useful.
Best Regards,
David Lo