Patch 1.21 improves compatibility with modern systems, which means that if you fancy poking around under the hood of Arx Fatalis, you can safely do so--without first risking your beautiful, beautiful skin attempting to remove the angry, clawing family of possums nesting there.
You can find the source code on FileShack, along with the patch. The full game, meanwhile, can nowadays be bought from Steam, GOG, Direct2Drive and elsewhere for around $5.
Arkane was acquired by ZeniMax Media--also owner of Bethesda, MachineGames, id Software and Tango Gameworks--in 2010. Their current project is presently a mystery.
Cheers to some chap named Nick Bredon from the Bethblog for the tip-off.