Keep it fast, simple and free. ASPajax is the definitive Ajax framework for Classic ASP (VBScript) websites. All you need is a W3C compliant ASP website and a few lines of code.
Following functionalities re available with the two packages. There`s a program code example that lets you execute VBScript server code from JS. Tool tips using ASP and AJAX are available and this lot converts the legacy code to AJAX easily. Similar changes for forms validation are another set that is available. Combo box control can be built using ASP AJAX. The combo Box can have predictive text suggestions. Implementing live chat that can be customized is also available.
Overall: Good set of tools to adapt legacy code to AJAX version. The coverage could have been more comprehensive, but a good star anyway.