Helpless agaisnt all things theme'd

[Kyris]

It's strange, but I've got quite a few problems with the themes.

My site: http://dreamersend.tzechean.com/index.php

Firstly, there's a drop down list of about 5 links of which are all called "Default". All display the same bland, basic page with the exception of the very last "default".

At this particular theme, there is a double repeat of the top links (you can see this in the link I posted).

Finally, which files should I be tinkering with to edit the templates to my liking?

Thanks so much for reading through, and I appreciate all the help I can get!