Of cource you can insert  your class' objects.
You should cast the object to its type  to be
able to access that class' methods and so on.

((YOURCLASSNAME)id.elementAt(i)).myMethod();

Vector accepts classes  of Object type, so you can add any object into that.
But when you retrieve object from that Vector, object will be in the form of
Object, so you need to cast it into your custom class. Then you can use that.
for example: ((myclass)id.elementAt(i)).myMethod();

Yes it is possible, but you have to cast the return value:

Worker worker = (Worker)workers.elementAt(i);
int salary = worker.getSalary();

Or you could start using Java 1.5, which has generics:

Vector<Worker> workers = new Vector<Worker>;
workers.add(worker);
...
int salary = workers.elementAt(i).getSalaray();

1) it would be better to use a Map implementation instead of a List
implementation,
2) make it using casting :
((YourObject)id.elementAt(i)).myMethod() etc...

why u prefer map than list in this case