Ok, I think I found a way to do thanks to Marc Clifton articale on 
CodeProject (http://www.codeproject.com/dotnet/MycroXaml.asp).

The XML file can be somthing like that:

<?xml version="1.0" encoding="utf-8"?>
<System Name="System">
    <Paramaters>
  <Speed type="System.Iint32">111</Speed >
  <_xAxis type="System.Single">222</_xAxis>
  <_yAxis type="System.Double">333</_yAxis>
  <_ID type="System.Int64">444</_ID>
  <_Name type="System.String">String value...</_Name>
    </Paramaters>
</System>


And the C# code can be:

System.IO.StreamReader sr = new System.IO.StreamReader("TypesDef.xml");
string text = sr.ReadToEnd();
sr.Close();
XmlDocument doc = new XmlDocument();
doc.LoadXml(text);
XmlNode node = doc.FirstChild;
while( node.NodeType.ToString() != "Element" )
{
   node = node.NextSibling;
}

XmlNode paramsNode = doc.SelectSingleNode("//Paramaters");
XmlNodeList nodeList = paramsNode.ChildNodes;
Hashtable verTypes = new Hashtable(nodeList.Count);
string typeName = "";
Type type;

foreach( XmlNode xmlNode in nodeList )
{ 
   XmlAttribute attr = xmlNode.Attributes["type"];
   typeName = attr.Value;
   if( typeName == "System.String" )
   {
      verTypes[xmlNode.Name] = xmlNode.InnerText;
   }
   else
   {
      type = Type.GetType(typeName, false);
      object typeIntance = Activator.CreateInstance(type);
      System.Reflection.MethodInfo Parse = type.GetMethod("Parse", new Type 
[] {typeof(String)});
      verTypes[xmlNode.Name] = Parse.Invoke(type, new object[] 
{xmlNode.InnerText});
   }
}

------
Regards
Sharon