before you say .htaccess, it really is php related!

I'm writing a cms from scratch, and right now my dynamic links look like this:

[...].net/forum/index.php?forum=$forum or ?thread=$thread
[...].net/mail/view.php?id=$id

and etc.

what I'd really like to do is
[...].net/forum/$forum/, [...].net/forum/$thread/, [...].net/mail/view/$id/

and have it be, if someone doesn't put a slash, rewrite it to automatically have one.

and for, once that's accomplished, have my user profiles be .../profile/$username and not have it specific as to lettercase (eg. accept tHetrend, thetrend, etc.)

also, cos right now I'm using dynamic as shown, and I use $_GET['id'] and etc in my coding. I don't know if that would be a problem, cos I know a few web 2.0-aware sites like rev.iew.me/ and despair.nu/ who have the format I'm interested in. thanks to anyone who can assist! =]