Err, sorry guys, I think I've figured it out already.
Anyway, 1 more problem here: same scenario, 2 files -> home.html & process.asp
Is it possible for me to do the data validation in home.html after the user presses SUBMIT, any errors must be corrected before submitting the form again to process.asp?
P.s: process.asp is another pop-up window.

Yes, but you'd have to use JavaScript to read the values of the text field. Even if you did this, it would not be secure enough because I could create my own form and view it from my home computer, submitting directly to your process.asp, which leads to my next answer...

Why don't you validate within process.asp? It's safer.

This error is strange. Are you using VBScript for your ASP page? If so, why does it give you a JScript runtime error? Do you have JScript running by default rather than ASP? Just curious.

Finally, I got a reply. I have done most of my coding, except for validation. I'm stuck! I am using ASP with jscript. The reason I do the client-side validation is because, based on what I have read about client-side validation, it's faster & only the correct data will be sent to the server to do further processing. Correct me if I'm wrong.
Err, I was using the Search feature provided by this forum & searched for
-> "client-side validation" & I got into the .NET Framework/ASP.NET forum. I realised that the problem posted there is similar to mine & so I posted my codes there. Would u mind checking it out over there? I apologize for the inconvenience.

Actually, client side validation is a nice thing to use, but should NEVER be relied upon.

Consider those that have JavaScript turned off!! How will you validate then?

I always handle validation on the server, as it makes more sense. If you know there is an error in the input, you just load up the form again (and because this is server side, there is no javascript) and can also do clever things like highlighting the problem input element.