半角カタカナをヘボン式ローマ字に変換するプログラム。
ルールは下記を参考にした。全部は実装していない。（手抜き）
 http://www.n-hirata-office.com/cgi-bin/n-hirata/siteup.cgi?category=1&page=3


Function romaji(kana)
  Dim k As String
  Dim n As Integer
  
  x = ""
  p = 1
  lens = Len(kana)
  While (p <= lens)
    k = Mid(kana, p, 3)
    x = x + romaji1(k, n)
    p = p + n
  Wend
  
  p = InStr(x, "ｯ")
  If (p > 0) Then
    Mid(x, p, 1) = Mid(x, p + 1, 1)
  End If
  
  p = InStr(x, "OO")
  While (p > 0)
     x = Left(x, p) + Mid(x, p + 2)
     p = InStr(x, "OO")
  Wend
  
  p = InStr(x, "OU")
  While (p > 0)
     x = Left(x, p) + Mid(x, p + 2)
     p = InStr(x, "OU")
  Wend
  
  p = InStr(x, "UU")
  While (p > 0)
     x = Left(x, p) + Mid(x, p + 2)
     p = InStr(x, "UU")
  Wend
  
  romaji = x
End Function

Function romaji1(kana As String, kanalen As Integer) As String
  Dim p As Integer
  
  kana3 = "ｷﾞｬｷﾞｭｷﾞｮｼﾞｬｼﾞｭｼﾞｮﾋﾞｬﾋﾞｭﾋﾞｮﾋﾟｬﾋﾟｭﾋﾟｮ"
  roma3 = "GYAGYUGYOJA JU JO BYABYUBYOPYAPYUPYO"
  p = InStr(kana3, kana)
  If (Len(kana) = 3) And (p > 0) Then
    romaji1 = Mid(roma3, p, 3)
    romaji1 = Trim(romaji1)
    kanalen = 3
    Exit Function
  End If

  kana2 = "ｶﾞｷﾞｸﾞｹﾞｺﾞｻﾞｼﾞｽﾞｾﾞｿﾞﾀﾞﾁﾞｽﾞﾃﾞﾄﾞﾊﾞﾋﾞﾌﾞﾍﾞﾎﾞﾊﾟﾋﾟﾌﾟﾍﾟﾎﾟ"
  roma2 = "GAGIGUGEGOZAJIZUZEZODAJIZUDEDOBABIBUBEBOPAPIPUPEPO"
  s = Left(kana, 2)
  p = InStr(kana2, s)
  If (Len(s) = 2) And (p > 0) Then
    romaji1 = Trim(Mid(roma2, p, 2))
    kanalen = 2
    Exit Function
  End If
    
  kana4 = "ｷｬｷｭｷｮｼｬｼｭｼｮﾁｬﾁｭﾁｮﾆｬﾆｭﾆｮﾋｬﾋｭﾋｮﾐｬﾐｭﾐｮﾘｬﾘｭﾘｮ"
  roma4 = "KYAKYUKYOSHASHUSHOCHACHUCHONYANYUNYOHYAHYUHYOMYAMYUMYORYARYURYO"
  p = InStr(kana4, Left(kana, 2))
  If (Len(kana) = 2) And (p > 0) Then
    p = (p - 1) / 2 * 3 + 1
    romaji1 = Trim(Mid(roma4, p, 3))
    kanalen = 2
    Exit Function
  End If
  
  kana5 = "ｱｲｳｴｵｶｷｸｹｺｻｽｾｿﾀﾃﾄﾅﾆﾇﾈﾉﾊﾋﾌﾍﾎﾏﾐﾑﾒﾓﾔﾕﾖﾗﾘﾙﾚﾛﾜｦﾝ"
  roma5 = "A I U E O KAKIKUKEKOSASUSESOTATETONANINUNENOHAHIFUHEHOMAMIMUMEMO" + _
  "YAYUYORARIRUREROWAO N "
  p = InStr(kana5, Left(kana, 1))
  If (p > 0) Then
    p = (p * 2 - 1)
    romaji1 = Trim(Mid(roma5, p, 2))
    kanalen = 1
    Exit Function
  End If
  
  kana6 = "ｼﾁﾂ"
  roma6 = "SHICHITSU"
  p = InStr(kana6, Left(kana, 1))
  If (p > 0) Then
    p = (p - 1) * 3 + 1
    romaji1 = Trim(Mid(roma6, p, 3))
    kanalen = 1
    Exit Function
  End If
  
  romaji1 = Left(kana, 1)
  kanalen = 1

End Function