Assuming that the letters represent names, and that each is in a separate paragraph, and that the second list (which bears no relationship to the first) is merely an example of what you wish to achieve then the following macro should work
Code:
Sub SplitList()
Dim oPara As Paragraph
Dim i As Long
Dim j As Long
For Each oPara In ActiveDocument.Paragraphs
If Len(oPara.Range) = 1 Then oPara.Range.Delete
Next oPara
j = ActiveDocument.Paragraphs.Count Mod 3
For i = ActiveDocument.Paragraphs.Count - j To 1 Step -3
ActiveDocument.Paragraphs(i).Range.InsertParagraphAfter
Next i
End Sub
http://www.gmayor.com/installing_macro.htm