Form with onchange function

I want to give option like pay by credit card or check.

If one select credit card in select option it opens credit card related form inputs/Check than check related form inputs before submiting form.

I would start like

<cfform action"" method=""Post>

<cfselect name="paymenttype" query="test" display="paymenttype" value="paymenttype">

<option value ="other">Other</>

</select>

<cfif form.paymenttype = "Credit Card">

<cfinput type="Test" name="creditcomp">

<cfelseif form.paymenttype = "check">

<cfinput type="text" name="bankinfo">

</cfif>

<input type="submit" value="Submit"></cfform>

I belive I need to use Java script onChange event but I never did Java script before, can any one help me on it?

I have been using cfcase and submiting form at each and than made session variable to generate appropriate result but now I wanrt to do some change.