OK. It didn't fully resolve my problem, but after moving the directions with the Xbox pad, the mouse sensitivity in Darwinia became normal for 30 minutes/1 hour. You may try this. The silence of Introversion about this problem is a shame : Darwinia is still sold on Steam and doesn't work well , godd...

Do you have a Xbox 360 controller plugged on your PC ?

I tried the 1.42 patch trick and it didn't work.

I triedd to reinstall the game, after deleting all data (including saves and preferences etc.) and it didn't work.

Please help !!

Same problem (Vista, Darwinia on Steam). The cursor in game is slow and erratic. The cursor is OK in the options, when I push Tab and on level select screen, the problem appears only in game. I tested, same problem on the first 3 levels. I'm not sure but I think it's worst when I choose low graphic ...