wtf is FISHY=""?
ajaxRequest('file.php', 'listid', 'POST', 'innerHTML', 'amount=' + javascript:document.getElementById('textboxid').value );
it shud be:
ajaxRequest('file.php', 'listid', 'POST', 'innerHTML', 'amount=' + document.getElementById('textboxid').value );
u use "javascript:" only when u call javascript over a link or as src of an html object.