Theme development

I'm getting ready to get my website online and for functionality I'm strongly leaning towards using a CMS, and thus why I'm here poking around the Drupal forums. What I'm trying to figure out in my CMS evaluation is what I'm going to be up against for getting my site incorporated with a CMS. What do I mean by that?

Is there an index of the available hooks/variables available that I can use to theme with using the PHPTemplate engine?

Something like this would be helpful;
- : description
$head - string:meta tag items that go between tags..
$logo - string:path to graphic file configured in admin > settings
$breadcrumb - array:provides site link bread crumbs in yadda yadda.. ( I think you get the idea )

Hi, I have searched into drupal.org site, but without lucky.

How can I change the user/register page ? I need to add some checkbox.

Tnx.

A user of my site (tbies.com) says there apears to be missing images in the Comments section of a story. Anyone know how I can get rid of these ghost images?

so the user name gets shortened in things like forum posts--to 14 characters, down from however many are in the name. This is true, and makes sense for a name like "supercrazylongusernamewowowow" which will display all kinds of weird, and great--cut it off. but for a user name like "super crazy long user name wow wow wow" why can't I get the whole name to display, and simply wrap where necessary?

Ideas?

Can anyone help me? User profiles appear way down a blank page at my new site tbites.com - and it happens with other things too like news aggregator. How do I edit the theme to stop this?