Everything I've always read about yams starts with the point that most people in the US confuse sweet potatoes and yams and that most US'ers probably have never had a real yam, despite the fact that Del Monte et al tend to label canned sweet potatoes as yams.
So: my suggestion to Joanna is find a real yam and cook it any old way, and some sweet potatoes too, just to see the difference and report back. Berkeley Bowl will likely have some. For me, I prefer sweet potatoes to yams.
/jordan