1998 Toyota Avalon XLS shaking?

My car shakes uncontrollably when I drive at 40mph, it's like being bounced on someones knee. I haven't driven it on the highway, seeing as I only got it the other day (free from my aunt), so I don't know if the shaking goes away at a higher speed.
So, just today, I had it serviced. I got new tires, and had the oil changed. The back struts are brand new, and the mechanic said the front ones are rusty, and that he can't tell what kind of shape they're in. Could this terrible distracting shaking be from the front struts? It's starting to freak me out, I thought changing the tires would help out a little bit, I guess I was wrong. The breaks are relatively new as well.