VB.NET
Public Function FromBin(ByVal Number As String) As Integer
    Dim pos As Integer = 1, l As Integer = Number.Length
    Dim Result As Integer, Current As Byte
    Do
        Current = Conversion.Int(Mid(Number, pos, 1))
        Result += (Current * 2 ^ (l - pos))
        pos += 1
    Loop While pos <= l
    Return Result
End Function
Public Function ToBin(ByVal Number As Integer) As String
    Dim Rest As Integer, Result As String = ""
    Do
        Rest = Number Mod 2
        Number = Number \ 2
        Result = Rest.ToString() & Result
    Loop While Number > 0
    Return Result
End Function

VB6
Public Function FromBin(ByVal Number As String) As Integer
    Dim pos As Integer, l As Integer
    Dim Result As Integer, Current As Byte
    pos = 1
    l = Len(Number)
    Do
        Current = CByte(Mid(Number, pos, 1))
        Result = Result + (Current * 2 ^ (l - pos))
        pos = pos + 1
    Loop While pos <= l
    FromBin = Result
End Function
Public Function ToBin(ByVal Number As Integer) As String
    Dim Rest As Integer, Result As String
    Do
        Rest = Number Mod 2
        Number = Number \ 2
        Result = CStr(Rest) & Result
    Loop While Number > 0
    ToBin = Result
End Function

VBS
Public Function FromBin(Number)
    Dim pos, l
    Dim Result, Current
    pos = 1
    l = Len(Number)
    Do
        Current = CByte(Mid(Number, pos, 1))
        Result = Result + (Current * 2 ^ (l - pos))
        pos = pos + 1
    Loop While pos <= l
    FromBin = Result
End Function
Public Function ToBin(Number)
    Dim Rest, Result
    Do
        Rest = Number Mod 2
        Number = Number \ 2
        Result = CStr(Rest) & Result
    Loop While Number > 0
    ToBin = Result
End Function

    Protected Function FromBin(ByVal Number As String) As Long
        Dim i As Integer, p As Integer = 0, Result As Long = 0
        For i = Number.Length - 1 To 0 Step -1
            If "01".IndexOf(Number(i).ToString()) = -1 Then
                Throw New Exception("Invalid parameter !")
                Exit Function
            End If
            Result += Number(i).ToString() * 2 ^ p
            p += 1
        Next i
        Return Result
    End Function
    Protected Function ToBin(ByVal Number As Long) As String
        Dim Result As String = ""
        Do
            Result = (Number Mod 2).ToString() & Result
            Number \= 2
        Loop While Number > 0
        If Result.Length = 0 Then Result = "0"
        Return Result
    End Function

Une fois optimisées c'est mieux ...

proc Dec2Bin {s} {
 binary scan [binary format I $s] B32 str
 return [string trimleft $str 0]
}
proc Bin2Dec {s} {
 set s [format %032s $s]
 binary scan [binary format B32 $s] I str
 return $str
}
# Tests
Dec2Bin 121
Bin2Dec 1111001