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By 'messing with a theme' did you actually work with a theme in the themes folder, or in the templates_c folder?
The templates_c folder contains temporary files. These files are usually created when someone visits a page for the first time. If you set the preference in admin to update module template.html files then the files are updated whenever there is a changed file in the current theme folder. It is good practice to use this setting when you're creating your theme, then turn it off when your theme is ready.
I suggest you delete everything in the templates_c folder, which will force XOOPS to create new cache files from your theme folder. If you included your graphics and backgound in the theme folder then that is what will be used. Also, keep that admin option on until your theme is ready, it makes it easier to see the changes you've made.
Hope this helps,
Rowd