Input key to hash password

[aspfun]

I used code below to hash password.

How to input key to hash, using letter or number?

Public Shared Function Encrypt(ByVal stringToEncrypt As String, ByVal key As String) As String
DES.Key = MD5Hash(key)
DES.Mode = CipherMode.ECB
Dim Buffer As Byte() = ASCIIEncoding.ASCII.GetBytes(stringToEncrypt)
Return Convert.ToBase64String(DES.CreateEncryptor().TransformFinalBlock(Buffer, 0, Buffer.Length))
End Function