UPDATE Feb 25, 2011.
After installing “Dead Space 2 PC Patch” from Feb 24, 2011 (link, link 2, link 3) it is possible to redefine movement actions to mouse buttons. However it is still not possible to assign other mouse buttons to other actions, for example back / forward in modern mouses like a R.A.T mouse. You need to use macro redefinitions.
Anyway, thanks Visceral Games / EA for a such fast patch! End UPDATE
The first impressions. Can not redefine movement actions to mouse buttons. This sucks. All the time error message appears – ‘Unable to assign that input’ – see last image.