I wouldn't try to be language neutral. Focus on a language like CFML or PHP which do this sort of thing very well. Eg.

<input type="radio" name="type" value='mortgage' onmouseup='updateForm(this)'> Mortgage <input type="radio" name="type" value='loan' onmouseup='updateForm(this)'> Loan <cfif form.type eq 'loan'> <input name="income" type="text"> </cfif> 

A very simple example. You could also use logic based on login details, database values, previous forms, etc.

I wouldn't try to be language neutral. Focus on a language like CFML or PHP which do this sort of thing very well. Eg.

<input type="radio" name="type" value='mortgage' onmouseup='updateForm(this)'> Mortgage <input type="radio" name="type" value='loan' onmouseup='updateForm(this)'> Loan <cfif form.type eq 'loan'> <input name="income" type="text"> </cfif> 

A very simple example. You could also use logic based on login details, database values, previous forms, etc. CFML also provides advanced form tags (eg, cfinput) which can take care of some of the messy details of dynamic forms for you.