I don't understand the last sentence, but you must be able to change the logo pretty easily by editing code (it's not feasible via Tiki interface). mod-logo.tpl is the file. I said you can't do it with Tiki interface but actually you may want to look at that "Edit Templates" item under Admin menu ;) It is Smarty code, but that's basically extended (or dynamic) HTML. And even if you didn't know HTML I think you would know how to change it
Something you will probably find useful for simple questions like this one is our IRC channel #tikiwiki.
It will be a pleasure to help you there