Javascript calculator

[psmoney]

Hey guys, On my website at psmoney.com I would like to replace my html forms with a java calculator so that a customer can enter any amount of money to trade. An example of what im looking for is http://www.cashmanbrian.com/mambo/index.php?option=com_content&task=view&id=34&Itemid=49

Please let me know if any of you can design something like that for me with the rates I wish to put in. I know this should be super easy for anybody that knows what they are doing.

Thanks