Old script not running in new browsers

Hi, I have been asked to look at an old conveyancing calculator as it no longer works (well not in all browsers, but most).
I know nothing when it comes to VBScript... can anyone answer why the script no longer works and perhaps a possible fix...
 
Sorry, the code is too long to paste in...

The example can be found at: http://geoffreylurie.com/convey_calc.htm

Hope someone can help me outta this dilemma

Thanks for looking

Well I would say that your first issue is that it isn't written in VBScript.