Is there any download link to the vc sa mouse tool that u can look around the player? :-\
If you really want to know what's going on behind your back just press the middle mouse key.
I have seen only a tool to control you actor & car with mouse (scroll up=accelerate, scroll down=brake :p). There was a similar question at gtaforums last time. Someone answered, that it may be possible, but for $$ ;). I however don't know how to do that, it needs probably some memory hack + other hacks = difficult to do. Sometimes it is possible to bug the camera and to move it like in SA (see: r1 + aim with e.g. M4, you were able to move the camera free).