Creating featured image (and thumbnail) from XML feed

hi All

i have a problem that killing me! Help would be greatly appreciated. i am using XML feed to create posts. XML feed have image, but featured image can NOT be added to XML.
How can I create featured image from external image that is specified in the XML?
And how can I create thumbnail of the featured image from external URL and place it on the homepage?

This is really critical for the current project. I am not coder, but marketing WP geek, so please let me know what need to be changed in which file. I hope there is a plugin for this, but I could not find one…

Cheers

Dean