It's not a simple conversion. Put "HDMI to scart converter" into Ebay, for instance, to see what is available. They seem to be about £20 or so.
Are you sure that the DVD player doesn't have more outputs? If there are yellow (video), red and black/white (audio) phono sockets on the back you can get a "phono to scart lead" for much less, about a couple of quid from a quick search I did.
EDIT - multiply beaten to it!