Right let me see if I can help at all.
On further inspection this afternoon I found the following.
I do not have a problem with things curving of the screen top to bottom so this may be a fault with the your tv. However..........Left to right i do have this problem. If I adjust the h-amp setting and stretch the picture outwards slightly the effect is reduced. I can make it go away completely, but using the over scan test pattern on digital video essentials, you have to put it past the 5% safe action line and so loose some of the picture in widescreen mode

. I have now come to an adjustment that just shows the 5% lines on the side of the picture and reduces the curving effect but it does not go away.
All I can say is try this and see what happens. Also if this worked on left to right try adjusting the v-amp so the picture stretches top to bottom and see if you can eliminate the other problem. Again it may or may not work.
I must just say that wide screen tvs and plasmas and rear projection displays all have there various problems so if you can not put up with your problem and want to exchange the tv for some thing else, you may have quite a hunt or your hands
I went through a 36" sony that had very good goematry but problems with r.g.b
A thoshiba 36" picture frame that had very bad left to right geomatry, so much so that the picture looked like it was sagging down to the middle of the screen.
A panasonic pd36" ( dont even get me started on that one
And now 2 loewe nemos 32an. Both of which had similar problems. ie picture distortion ,geomatry errors and dirty picture syndrome.
I am gona put up with this untill christmas and then try and find a half decent plasma
(got to get the kitchen and bathroom done first

)