A few eearly 320d in Germany had a similar problem. It was a broken engine mount / vibration damper. The symptons (shudder) were simmilar to yours.
German dealers were advised to not let a customer leave with his car once the problem was diagnosed. There was a (slient) recall for the issue It was deemed to dangerous to drive because further damage to the car could occur. Basically the engine can move too freely in the engine bay, meaning that fuel pipe, water hoses, maybe even the exhaust can tear /break. Only happened on y afew earyl cars though.
As far as I remeber you have a relatively early 320d so you might be into the same trouble.
I would not drive the car for longer distances and I would call BMW headquarters for them to look into wether or not there is a bulletin in your country for the problem. Book into a different dealer if you have to or go back to the original dealership and INSIST on priority treatment. Try to find a good mechanic that will put priority on safety and avoidance of further damage instead of keeping some kind of shedule.
This may be serious enough to really stink up the dealership if nessecary.
In short, raise hell if you want to prevent further damage to your car.
(But allways in a curtous and kind manner, that´s way more effective. You´d be surprise what gets done when you kindly refuse their offerings and simply not leave until the problem is satisfactorly taken care off)
In these links you´ll find some posts in german forums about the vibration damper Problem (Schwingungsdämpfer) for what it´s worth
http://www.motor-talk.de/showthread....gungsd%E4mpfer
http://www.motor-talk.de/showthread....gungsd%E4mpfer