I used to have a apple tv 1st. gen with a beosystem - used the atv hack from firecore:
http://firecore.com/atvflash
There are other methods as well - something like composite hack?
Take a look at this or this (so using composite / rca to scart).
Ralf
My Beo: Beosound 3000, Beolab 4000, Beo 4 DVD, Beolab 5000/Beomaster 5000, Beovox S45.2 with Stands, Beosystem 7000 black with Beolink 7000, Beolink 1000, F1000 (3 cubes), Beovox 5000, Beovox 3000, Attyca 1.