I have been seeing lots of cute sheath dresses and shirt dresses in stores for spring, but as a curvy girl, they are not working for me. Am I doing something wrong? Is there a trick to making them look like something other than paper bags on me, or should I just stick with what works?

Examples:
http://bananarepublic.gap.com/.....=949892002
This dress would look frump-tastic on me, but looks so carefree.

Cute sheath, and besides it being too short, how do I make this look like I'm not a big block? In order for it to skim my body like it is here, I have to buy up a size so it's not a clinger, and then it looks bad.
http://bananarepublic.gap.com/.....=949949002

This is my typical dress shape, but I don't always want to be so vavavooom at the office -- but there is no way this shape of dress fits me and it's NOT bombshell. I always need a jacket or sweater, and that's no fun!
http://bananarepublic.gap.com/.....=932442002