Display software

[werner]

I am currently considering the possibility to display structures
which are deposited in the Brookhaven databank on a MacIntosh (Quadra 700).
I would like to know if freeware programs able to do that and also 

eventually to do some modelling (i.e. replacing one amino acid by another).
I do not know if such programs exist for the Mac or even if it the 
machine is powerful enough for that purpose. The program should also
be simple since I do not know much about modelling.
Any suggestion would be welcome.

Michel Werner
Service de Biochimie et Genetique Moleculaire
Batiment 142
Centre d'Etudes de Saclay
F-91191 Gif-sur-Yvette
France

werner at jonas.saclay.cea.fr