[plt-scheme] Load and require in PLT

Hi guys,
I am trying to find an equivalent way to run the following test.scm
script with mzscheme.
I would like to to keep s as a variable, so that it could be passed as
a command-line argument.
(require "parameters.scm") works in mzscheme while (require s) does
not. From what i gathered from reading the plt archives using units
could be the way to do it ...
Help will be very much appreciated!
Nik

csi test.scm

;; test.scm
(define s "parameters.scm")
(load s)
(display  x)


;; parameters.scm
(define x 1)