Problems with Featured Images

Hi everybody,

I want to have featured images for my posts on the frontpage, and I want them with a height of 200 px. When I upload the images, they have a height of 200 px.
But when I go to my frontpage what I see is the same picture with another dimensions.
I have used firebug to see which CSS may solve the problem, but I wasn’t successful.
Can you settle the dimensions of the featured images with wordpress? How could I control this?

I need your help.

Another issue with the featured images is that I don’t want them in my posts (only on the frontpage), and they appear at the beginning of the posts.

Do you have any idea?

Thanks in advance,
David