I just went through the very same thing - wanted a digibox specifically for the projector.
All digiboxes with scart outputs will output a 'video' signal so yes you can just buy a scart adaptor and plug it in. It will look impressively big on your wall. But what you want though is one that gives you a component signal because this is much better. I don't mean a tiny bit better so only videophiles will notice, I mean eliminating all the little crawling dots and getting a noticeably higher quality stable sharp picture.
Most (all?) new digiboxes have an RGB mode, but the AE100 does not take a 'TV' (R,G,B) signal, it wants a component signal (Y,Cb,CR), or a PC (ie monitor socket) signal. The only box that can be set to output component from its scart socket is the Netgem I-Player. Actually BT do an own-brand model which is based on it, but nobody else does.
Then you get a scart to component cable (scart to 3 phonos, for the video output to the projector) and a digital optical cable or 2 regular phonos (for the audio to your hifi or speakers).
The BT digibox is on offer at the moment at
http://www.shop.bt.com/icat/btdigitaltv and is a real bargain at 64.50. It also has a built-in modem to do web browsing on your TV/projector, plus a USB port to allow you to connect your PC for broadband web browsing on your TV/projector. Nice additional features but I only bought it for the good quality output.
For the scart to component cable I bought a Profigold PGV372 from
http://www.tvcables.co.uk - about 18 quid, but worth it (and cheaper than elsewhere)
Hope this is useful. Yes you can use a normal Video signal (scart to single yellow phono output), but it looks crap ; you could use S-Video (scart to funny little 4-pin plug) which is pretty good but not as good as it could be; component is the best and unless you have a high end DVD player the PJ component sockets will be empty!