how to make Windows forget my passwords?

when I access my email (and a few other programs) thru the web browser, Windows XP “does me a favor” and automatically fills in my username (after I type the first letter).
Then the password gets filled in automatically, too (showing black dots instead of the actual letters, but what difference does it make?)-anybody who knows the first letter of my username gets logged in automatically.

Apparently, I once clicked “yes” on that irritating dialog box “do you want Windows to remember this password for you?” .
Well, I want to UNclick that option. How do I do it?

Your browser does that, not XP. Assuming you’re using IE, go to Tools > Internet Options > Content tab. Click the AutoComplete buitton and uncheck “User names and passwords on forms”.

Is there any way to do this for selected passwords? I’ve got several that I’m quite happy to have filled in for me, but I’d like a little selective amnesia as well.

Not that I’m aware of. Or rather, not directly. You can click Clear Passwords to erase ALL of them, and make sure that “User names and passwords on forms” is checked as well as “Prompt me to save passwords”. Then you can start fresh, as it were by telling it which passwords to save and which never to bug you about again.