proportional editing...

OK, why are these vertices moving, and how can I get them not too? Can I get the proportional edit field to be 2 dimensional? I am pulling only the bottom vertices. I want the top vertices to remain in place, so when facing directly in front, the entire object will appear to be rounded around the edges

http://img364.imageshack.us/img364/2872/wtfyd9.th.jpg
http://img364.imageshack.us/img364/9841/wtf2cs7.th.jpg

So I had to do a hack. Basically, I shrunk it down on the y axis by .001, applied the proportional edit along the x axis, and then scaled up on the y axis by 1000. It just doesn’t feel right, and it doesn’t feel like this is the way I used to do this. I am so frustrated something so simple has caused me so much trouble. X( Something doesn’t feel right!!

http://img337.imageshack.us/img337/6285/hackae6.th.jpg