The MailToURL function creates a mailto: url that can be used to create a mail message, complete with a subject and body already intact. Take a look at the sample code for sample usage.
Public Function MailToURL(sAddy As String, sSubject As String, _
   sBody As String)

    MailToURL = "mailto:" & URLEncode(sAddy) & "?subject=" & _
       URLEncode(sSubject) & "&body=" & URLEncode(sBody)

End Function

Public Function URLEncode(sPlain As String) As String

    Dim i As Long

    For i = 1 To Len(sPlain)
        Select Case Asc(UCase(Mid(sPlain, i, 1)))
            Case Asc("A") To Asc("Z")
                URLEncode = URLEncode & Mid(sPlain, i, 1)
            Case Else
                URLEncode = URLEncode & "%" & _
                   Right("00" & Hex(Asc(Mid(sPlain, i, 1))), 2)
        End Select

End Function
Sample Usage:
Private Declare Function ShellExecute Lib "shell32.dll" Alias _
   "ShellExecuteA" (ByVal hwnd As Long, ByVal lpOperation As _
   String, ByVal lpFile As String, ByVal lpParameters As String, _
   ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long
Private Const SW_NORMAL = 1

Private Sub Form_Load()

    Dim sAddy As String
    Dim sSubject As String
    Dim sBody As String
    sAddy = ""
    sSubject = "Example Message"
    sBody = "This is just an example message" & vbNewLine & _
            "Please disregard"

    ShellExecute 0, "open", MailToURL(sAddy, sSubject, sBody), _
                 "", "", SW_NORMAL

End Sub