Question

I have a custom site definition, in an ONET.XML file.
Can I get the URL and/or the Site name of the site that is being created and use it as a parameter/moniker in the onet.xml file?

Something like this:

 <Modules>
    <Module Name="Default" Url="" Path="">
      <File Url="default.aspx" NavBarHome="True">
        <AllUsersWebPart WebPartZoneID="Right" WebPartOrder="1">
          <![CDATA[
                   <WebPart xmlns="http://schemas.microsoft.com/WebPart/v2" xmlns:iwp="http://schemas.microsoft.com/WebPart/v2/Image">
                        <Assembly>Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c</Assembly>
                        <TypeName>Microsoft.SharePoint.WebPartPages.ImageWebPart</TypeName>
                        <FrameType>None</FrameType>
                        <Title>[NAME OF MY SITE] or [URL]</Title>

Answer 1

Not to the best of my knowledge.
I have used a solution where I add the webparts programmatically via the WebPartManager and then to set properties on that WebPart I use reflection.

An example to add the WP to a page:

public static void AddWebPart<T>(string webPartZone, SPFile page)
{
    Type wpType = typeof(T);
    AspNet.WebPart webPart =
        (AspNet.WebPart)wpType.GetConstructor(new Type[0]).Invoke(new object[0]);

    try
    {
      page.CheckOut();                                               
      SPLimitedWebPartManager wpManager = 
         page.GetLimitedWebPartManager(AspNet.PersonalizationScope.Shared);
      wpManager.AddWebPart(webPart, "WP Zone Name", 0);
      page.CheckIn("Added web part", SPCheckinType.MajorCheckIn);

and here is how to set proprties on webparts:

public static void SetWebPartProperties<T>(Dictionary<string, string> properties,
                                           SPFile page)
{

    Type wpType = typeof(T);

    SPLimitedWebPartManager wpManager = 
    page.GetLimitedWebPartManager(AspNet.PersonalizationScope.Shared);

    foreach (AspNet.WebPart wp in wpManager.WebParts)
    {
        if (wp.GetType() == wpType)
        {
            foreach (KeyValuePair<string, string> kvp in properties)
            {
                System.Reflection.PropertyInfo pi = wpType.GetProperty(kvp.Key);
                if (pi.PropertyType == typeof(int))
                    pi.SetValue(wp, int.Parse(kvp.Value, CultureInfo.InvariantCulture), null);
                else if (pi.PropertyType == typeof(bool))
                    pi.SetValue(wp, bool.Parse(kvp.Value), null);

                pi.SetValue(wp, kvp.Value, null);
            }
            wpManager.SaveChanges(wp);
        }
    }
    page.CheckIn("Changed properties of webpart", SPCheckinType.MajorCheckIn);

}