Dreamcast SCART Cable

You can get SCART to Composite adaptors, but they're not that common. It'll probably easier to get a composite cable instead.

Something like this would do, but the proper cable is likely cheaper

Late (but hopefully on-topic)

I have a recently acquired HDTV and I have a Dreamcast but I use the standard RF cable that comes with it, the quality isn't terrible but you can definitely tell the difference between it and composite.

However, I can't tell you how much fun it was having to manually tune the TV to find the correct channel for the Dreamcast, haven't done that in years

Very late I know, but in regard to the last post.

I don't think it is RGB, since posting here I have bought an RCA (Yellow, White, Red) cable and that works very well except that it still looks a bit naff on an LCD TV.

I think if any Dreamcast users have HDTVs they should really fork out for one of those VGA boxes, but only if they really want the higher quality, otherwise just use a CRT TV.

Just realised I sort of rambled there...

TL/DR: I don't think the scart cable is RGB, I could be wrong though.