Sorry for bad english.
After update from 2.7.1 to 2.9.2 have problem like you all.
I try pached files from there:
it was bad thing, editor show only styles.css.
What i did, its just workaround.
Downloaded again wordpress 2.9.2, grab theme-editor.php, plugin-editor.php and misc.php
edited "theme-editor.php" at line ~173 and ~191
this line part of generating theme files list and adding bad link to each. So i add string with part of url was missing.
<li><a href="theme-editor.php?file=<?php echo "/xxx/xxx/xxx/wp-content".$template_file; ?>&theme=<?php echo urlencode($theme) ?>&dir=theme"><?php echo $filedesc ?></a></li>
for finding what URL part you missing, just use "Update" button in editor, then look at adress bar and diff with theme file link in sidebar.
for now its good, but its just stupid workaound,
if i get some time im will search solution of problem.