When using the xhtml1-transitional.dtd
doctype, collecting a credit card number with the following HTML
I would be very surprised if W3C would have proposed a way that would work with (X)HTML4. The autocomplete feature is entirely browser-based, and was introduced during the last years (well after the HTML4 standard was written).
Wouldn't be surprised if HTML5 would have one, though.
Edit: As I thought, HTML5 does have that feature. To define your page as HTML5, use the following doctype (i.e: put this as the very first text in your source code). Note that not all browsers support this standard, as it's still in draft-form.