Coilovers/?

[clb0099]

I had 19" brand new wheels mounted and balanced as well as installed on my 1997 Porsche boxster. After going on the highway and hitting 70 mph and above the steering wheel shakes violently. It use to shake with the stock wheels but was very little even not noticable . My question is I already bought coilovers which are not installed. I also bought brand new front wheel bearings . The question is a two fold one. First what the hell could it be making the steering wheel to shake like this... bearing? ball joint? tie rod? How would I test to see what it is? The second part of the question is how much it cost me to install coilovers exclude a car alignment?