I recently got a '96 Bonneville, and I've got two main problems with it. The lesser is that the steering is pretty tough after about a 60 degree turn. The more important one, however, is that when idling, the engine shakes pretty badly. Just in drive, though, if you put it in park it calms down. I'm new to working on my own vehicles, but I'd like to give it a try if it'* plausible. A friend who looked at it said the belts may be cracked and loose. I'd assume that'* a contributing factor, but I'm green in the area. Any suggestions? Thanks in advance ~

I have no idea bout the steering issue.. but first thing I would look is probably the Tie Rod ends..but I"m probably way off base on that one.

regarding your violent idle shake. It'* obviously doing it under load (in drive).. but does it do it in O/D ?? When you lightly get into O/D speed ( no idea what that would be in miles.. but probably around 80ish KM/H unless it'* the supercharge version which would be around 70km/h )
At the lowest RPM to hold it in O/D.. slowly step down on the gas ( but not to the point it downshifts ).. does your car bog down or stumble/hiccup then?
Another thing to check is have a friend put the car in drive and hold the brakes down.. when your engine is shaking violently.. check the motor mounts..

I don't know if vacuum leaks will only affect it at idle only.. but someone can give you better idea

How many miles / km'* are on the car? It sounds like it needs a tune-up IMO