dude your pointing to the wrong URL somewhere..
where is your additional theme located? where is it in relation to the other theme that you mentioned? (and assuming the other theme displays the img's correctly)...
Are the themes peers as far as directory structure in concerned? or are they in different directories?
here is a really easy way to play... copy the directory which has the functioning img files in it so it's on your clipboard..
go the the exact place your residual HTML (your page as seen in a browser) points to when looking for image files.. note it..
find in your web structure that exact place.. paste your directory with the img files there.. if it works, your theme is simply referencing the wrong place while calling img's.. which is what it looks to me is happening.