linear motion and power

hello, Got 2 questions:
(1) I need to be able to move a 5x3x3 rectangle 4 inches (it is on linear
rails) one way (gravity will make it go back the other 4 inches).
The only problem is, it cannot go from point A to B in 1 second.. it needs
to be gradual.. around an inch a second or so.
I was thinking of spring loading it.. but i think that would still be to
powerfull
then thought about some sort of pnuematic device.

any ideas?

(2)I bought:
http://www.allelectronics.com/cgi-bin/category.cgi?category=480&item=PS-2465&type=store

I measured + and - output and looked like it was outputing 24vdc.. I was
wondering, could I hook up 2x 24vdc devices? or 2 x12vdc devices?

thanks!-Lee