Rewrite all requests in the form of:
^([a-z0-9]+)/login/?$
to something like:
/phpfiles/login?user=$1
where [a-z0-9]+ should be replaced with whatever pattern you use to define a valid username.
EDIT: For clarification, when I say "rewrite," I am of course referring to Apache's mod_rewrite (or similar module/plugin, depending upon your webserver of choice).
