I had the urge to dust Omikron off a week or so back and attempt to get it running under Windows XP again.
Didn't need much tweaking at all, believe it or not. The install went smoothly (I chose full install). I also got rid of the runtime error at game startup. I'd previously tried just about everything to get past it, including using compatibility mode.
The problem are the movies that are in the FLIS folder. For whatever reason, WinXP just doesn't like the format they're encoded in.
Just create blank text files that use the names of the respective movies. When you save the files, change the extension from TXT to MPG. Replace the movies in the FLIS folder with the blank text files.
The three movies are fairly inconsequential anyhow. They are the Eidos logo, Quantic Dream logo and Quenta Cola commercial with Omikron logo at the end.
The vital cutscenes are rendered in game. Everything ran smoothly on my set after that. The sneak can be a little slow, but not enough to degrade the game. The graphics looked great at full 1440x900 resolution.