Learning to build joomla templates takes a little time.
Have you read this - strating point:
http://docs.joomla.org/Tutorial:Creating_a_basic_Joomla!_templateI would start tinkering with one of the defaulst templates css and index.php file to see how it all "works" - in fact you could actually change ANY template to look like you wnat - but you need to tinker with html / css and php code.
Use firefox browser with firebug plugin - do you know these.
If I were you I'd start with a test site and spend some time with the rhuk milkyway template. Then go template hunting - find something similar and make changes as needed.
You may also be interested in a program called artisteer [
www.artisteer.com/ ] - but I personally prefer hadnd-coding templates
