How we can compare to XML files.

You can write your own xml files comparer so that every time you need to compare two xml files you make use of this magic class
public class XmlComparer : IComparer
        {

            public string FirstFilePath { get; set; }
            public string SecondFilePath { get; set; }
            public int Result = 0;
            
            #region IComparer Members

            public int Compare(System.Xml.XmlDocument x, System.Xml.XmlDocument y)
            {
                x.Load(FirstFilePath);
                y.Load(SecondFilePath);
                /* Then you do compare the two files, I don't know the
                 * comparaison your criteria exactly is it the lenght or other criteria*/
                if(/*Condition1*/)
                {
                    Result = 0;
                    return Result;
                }
                else if(/*Condition2*/)
                {
                    Result = 1;
                    return Result;
                }
                else
                {
                    Result = - 1;
                    return Result;
                }
                //Then you can make the decision based on the
                //Result value, this is the magic effect using
                //The generic with the comparer interface
            }

            #endregion
        }

One way you could do is, load two XML files into two DataSet objects using DataSet.LoadXml method. After that, you can compare two DataSets. Read here:

http://www.devnewsgroups.net/group/microsoft.public.dotnet.framework.adonet/topic16270.aspx