The naming of the XML-Tags has nothing to do with the used Java-Class. So keep your log4j.xml. The javadoc of Category (Log4J 1.2) sais:
-----8-<------------8-<------------8-<------------8-<-------


This class has been deprecated and
replaced by the {@link Logger} subclass. It
will be kept around to preserve backward compatibility until mid
2003.

Logger is a subclass of Category, i.e. it extends
Category. In other words, a logger is a category. Thus,
all operations that can be performed on a category can be performed
on a logger. Whenever log4j is asked to produce a Category object,
it will instead produce a Logger object. However, methods that
previously accepted category objects still continue to accept
category objects.

For example, the following are all legal and will work as expected.

      // Deprecated form:
      Category cat = Category.getInstance("foo.bar")

      // Preferred form for retrieving loggers:
      Logger logger = Logger.getLogger("foo.bar")
   

The first form is deprecated and should be avoided.

-----8-<------------8-<------------8-<------------8-<-------

So your config file keeps. But use Logger instead of Category in your code.