Theme development

Hi,
I am new to drupal. i am not aware what are these .tpl.php files for?
By creating a new .tpl.php file how can it be invoked in a module.
For example I have found that by defining a profile.tpl.php within the current theme's directory , the profiles are displayed in a different way.

Is it predefined that if a .tpl.php file is created with the name module_xx.tpl.php then every time the module_xx is
invoked this file will be called?

Is theming something that is usually done once, or does it need a lot of continual upkeep as new modules are added?

I see a site with theming that I like. Do I have enough info from the html source and the css files to sort of replicate? Is it fairly easy to copy a site, or is it hard?

Hey - I've got a weird application I was building in flash -- had a builder spitting out xml, and a playback app playing back all these screens - but I'm thinking about switching it to drupal..

The basics are there are 2 types of screens - home and subscreen -- where

home screens
-- has 2- 8 'slices' where there's a different background img for each slice, multiple buttons per slice
subscreen
-- full background image
-- 1 - 3 columns of text with a translucent color over the background.

In the node create/edit form, what is the best way to make the 'Image Galleries' taxonomy dropdown field appear seperate from the rest of the categories (i.e. not in the Categories fieldset)?

Most people write code as:

<?php if ($sidebar_right) { ?><div id="sidebar-right">
      <?php print $sidebar_right ?>
    </div><?php } ?>

But I think that right code must be written like this:
<?php if ($sidebar_right) print "<div id=\"right_side\">".$sidebar_right."</div>" ?>