JS, ASP: Best way to validate? easy [resolved]

[invitro]

Ok here is the plan:

PageA.asp has a form. On that form I have

txtUser
txtPassword
cmdSubmit

After hitting submit, user gets redirected to PageB.asp where the result (user data) is stored in a database.

Now, what is the best way to validate that the user has filled out all the fields.

Do I do it in PageB.asp or PageA.asp
I was thinking of embeding a simple JS function into

<FORM ACTION="JS FUNCTION HERE">
</FORM>

Is that possible? Is that a good way of doing it, or does it have something to do with the actual Submit button.

I'm also pretty sure I could check the values on PageB.asp, to see if they are blank and display an error... would that work?

Thanks a lot,
InVitro