Not totally clear on the question, however:

1) If you don't want images in your excerpts, I would recommend installing the "Advanced Excerpt" plugin, which can be found on the WordPress Extend website. From there you can disable all HTML or IMG tags inparticular, so they are not displayed in any excerpts of the website.

2) If you want to use a smaller image in the main blog post, and a larger one once they hit 'read more'. I'm not positive on that. I believe there is a plugin to accomplish this, but I'm not sure. There is also some fancy footwork you could do with the post-thumb plugin, but would require some effort and customizing.

Hope that helped.

Yes, you can disable images in excerpts including the 'latest' area via the plugin I mentioned above. You also can use a content_rss call and limit the words output, sort of like an excerpt, but that runs into other problems sometimes.