Theme development

theme () function is initializing the theme layer and dispatching of function calls to the appropriate places, in that case how it works?
i.e how these file are involving theme.inc at include directory, theme engine etc.

theme system of drupal consist of components as listed below.
Template languages, theme engine, and themes.
can any one pls explain me how these thing are related and when we add new theme to drupal how it works?

I am making great progress on my home page but it occurred to me that I will want to have customized themes for other pages. I want each page to look slightly different than the next.

For example, I want my login page to look slightly different from my home page, help section etc. I also want a to place a purchasing form page that is secure.

I’m a little confused on how to make drupal do this without going through "creating content/node".

Basically this site seems to do what I want

http://www.hipfoto.com/

This is my first theme for drupal and i cant seem to make the rounded corners work?

The only way i can is to use tables and i would rather use DIV's:

Screenshot

I'm trying to add an image tag to the page.tpl.php form and it's not showing up. can anyone tell me what i'm doing wrong? Are you allowed to add html image tags to the tpl.php files?

I'm having some difficulty with a possible z-index problem in IE 7 and most likely 6.
Here is the page I'm setting up
http://www.nationalwind.com/why_national_wind
The test header is a block and it's on top of my nice menus block.
I want that order flipped.

Any thoughts...