No that will not work. You have to look through the css. Find every image url in it. Look in the folders for the theme you downloaded and find those exact image files. Upload them to an image host. Get the direct url for them and replace the urls in the css. Yeah its a lot of work but its the only way you can do it.
Make sure the theme is for smf2.0 That is the only version that will work. And again: if the theme has changes to the template(s) you wont be able to use it and get the result you are looking for.