just a snip..
Dim myDWG As ApplicationServices.Document = ApplicationServices.Application.DocumentManager.MdiActiveDocument
Using ML_Trans As DatabaseServices.Transaction = myDWG.TransactionManager.StartTransaction
Dim myDB As DatabaseServices.Database = myDWG.Database
Dim myMLeader As New DatabaseServices.MLeader
Dim myMLStyleDict As DBDictionary = myDB.MLeaderStyleDictionaryId.GetObject(OpenMode.ForRead)
myMLeader.MLeaderStyle = myMLStyleDict.GetAt("Style1")
Dim bt As BlockTable = TryCast(ML_Trans.GetObject(myDB.BlockTableId, OpenMode.ForWrite), BlockTable)
Dim btr As BlockTableRecord
If ApplicationServices.Application.GetSystemVariable("cvport") = 1 Then
btr = TryCast(bt(BlockTableRecord.PaperSpace).GetObject(OpenMode.ForWrite), BlockTableRecord)
Else
btr = TryCast(bt(BlockTableRecord.ModelSpace).GetObject(OpenMode.ForWrite), BlockTableRecord)
End If
btr.AppendEntity(myMLeader)
ML_Trans.AddNewlyCreatedDBObject(myMLeader, True)
ML_Trans.Commit()
End Using
**Disclaimer: has not been tested **