Theme development

I active Clean URLs and it is working.

but i use follow code on theme, it do not return a clean URLs (?q=logout):

l('user logout', 'logout', $attributes = array('title' => t('logout'));

how to return clean URLs ?? (/logout)

Oops, accidentally posted this in the developers forum. Not clear where this should go, but I'm getting nowhere searching the forums or browsing the API docs ...
Is there a Drupal variable of some kind available that simply indicates whether the current user is logged in or not?
Better still, is there a document somewhere that details this and all similar variables?

I've set up Drupal 5.5 to use a standard theme for admin (Minelli) and a custom theme for the front end.
This is working well enough except for one issue.
While in the admin area, if I go to Create Content, the theme suddenly switches to the custom theme.
Any pointers to what I or Drupal may be doing wrong?

Hey guys and gals & thanks for reading this,

I have been searching for a solution everywhere; this site of course, as well as a google search with site:drupal.org. But found nothing promising. My problem is:

I am using the most recent version of 5.x. I have created a CCK content type, and a unique node-content.tpl.php file to control output. Each of these content pages is also outlined in a book, using the outline.module. However, at the bottom of the page, where the book page navigation usually appears, there is no navigation. On non-unique content nodes (page, story) the book page navigation appears correctly.

I am using a custom theme FOR MY PROJECT. I enabled the search block, but had to view the source because the class names I used in my style sheet were different. I had to use block-search-0 as the class id in order to get it to work. I looked at all the style sheets that were being imported, but don't see where this is comming from. There is only one style sheet in my theme folder - mine. I don't want to change anything in the module code because I'm sure I'll be updating to 5.6. Also, the search block disappears entirely when viewed in firefox.