thumbnails issue

Hi BHW.......
Can someone tell me how to display thumbnails for posts like in thumbnails on the sites like

For few posts the thumbnails are small and for few they are large as in a full post....

If it is a plugin or what......
Please help me with this.... will be great help
Thank you

I think it's manual setting in from the post. If thumbnail, you can set at setting, media. You can manage your thumbnail as you like.

Even, I can use the thumbnail for excerpt content too. Look at my autoblog nasimage. I use thumbnail excerpt. I can manage them from setting, media in wp. you can download plugin here cnet[dot]ro/wordpress/thumbnailforexcerpts/

Oh ya, my blog is dot com ;p
Hope that help you. Thanks