Converting simple VB to JScript

Hello I have the following form in a VB Program

Total CP:  <Textbox name="txtCP">
Total XP:  <Textbox name="txtXP">
Silver:    <Textbox name="txtSilver">
<CommandButton name="cmdCalculate">
Earned CP: <Textbox name="txtCPGot">
Earned XP: <Textbox name="txtXPGot">

What I want to do is recreate this form and it's functionality in an HTML Page.  I've created the form with onclick="CPCalculate()" for the command button.
What I need is the following Visual Basic code converted into JavaScript code that will work on IE4 and Netscape4(if possible).  This form will not make a round trip to the server just Calculate the answer on the client side.

Well here is the VB code for CPCalculate

Private Function FigureCPCost(ByVal Level as Integer, ByVal Which as Integer) as Integer
  Dim Modifier as Integer
 
  Select Case Level
    Case 1: Modifier = 5
    Case 2: Modifier = 10
  end select

  FigureCPCost = Modifier * Which
end function


Private sub CPCalculate()
  Dim Total, CPCount, Level, Extra, Which
  Dim CP, XP, Silver

  if txtCP.text="" then txtCP.text = "0"
  if txtXP.text="" then txtXP.text = "0"
  if txtSilver.text="" then txtSilver.text = "0"

  CP = txtCP.text
  XP = txtXP.text
  Silver = txtSilver.text
  CPCount = 0
  Total = CP + XP + Silver
  Level = ((CP - 25) \ 10) + 1   'notice the \ for integer division
  Extra = (CP - 25) mod 10
  Which = 1

  do while Total > FigureCPCost(Level, Which)
    Total = Total - FigureCPCost(Level, Which)
    CPCount = CPCount + 1
    Which = Which + 1
    if Extra + Which > 10 then
      Level = Level + 1
      Extra = 0
    end if
  Loop

  txtCPGot = CPCount
  txtXPGot = Total
end sub