Don't want to spoil your fun but there are various functions out there that will alrady do this:
e.g.
Function URLDecode(ByVal pstrIn)
Dim p
pstrIn = Replace(pstrIn, "+", " ")
p = InStr(1, pstrIn, "%")
Do While p>0
pstrIn = Left(pstrIn, p-1) & Chr(Cint("&H" & Mid(pstrIn, p+1, 2))) & Mid(pstrIn, p+3)
p = InStr(p+1, pstrIn, "%")
Loop
URLDecode = pstrIn
End Function