SOS Journalist need help, stupid problem, image not shown

Dear Drupal Community

I am not programmer, I just crazy militant journalist, who learn Drupal because we need it immediately but no money :) to hire competent programmer, may be next time, i hope can hire excellent programmer to exoduse me from the learning curve syndrome. The only script that i know is autolisp for dos because i am oldish architect also, is not help because Drupal is PHP

I installed image 6.x-1.0-alpha4 plus image Image Assist, on debian linux hosting, spanel cgi. Folder image mode 775, public. The problem is image not shown in page, the only shown is title, i tray find path with firebug:
http://www.silih.org/sites/default/files/images/logo_0.thumbnail.png
then, the browser respond is "Internal Server Error:

then i try change
http://www.silih.org/system/files/images/logo_0.thumbnail.png
then, bingo the image is shown, but how i change the path on image assist module? is it brute hack method?

image cache module had some problem, also

it make me frustrated, on my Ubuntu linux or XP at home it work properly, but lose the way on hosting place, i had communicated with the technical but still not not yet solve the problem.

Other info
Share hosting
Her we go some setting on my hosting:

default htacces that permitted to use:

Order allow,deny


Order allow,deny

ErrorDocument 404 /index.php
##direktori index sebetulnya sudah default
DirectoryIndex index.php

ExpiresActive On
ExpiresDefault A1209600
ExpiresByType text/html A1


RewriteEngine on
##drupal terinstal di direktori mana relatif
##terhadap root document. jika ada di root document
##tulis RewriteBase seperti di bawah ini.
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]

if i use default httacces from drupal it not all permited for some security puropse

Php.ini

; ini hanya contoh, silakan diedit sendiri

; masih banyak aplikasi php yang membutuhkan ini
register_globals = off

; extension yang paling umum dipakai. untuk kinerja terbaik, hanya muat yg anda butuhkan
extension=mysqli.so
extension=mysql.so

extension=pdo.so
extension=pdo_mysql.so
extension=gd.so
extension=curl.so

memory_limit = 98M
;
; daftar extension lengkap dapat dilihat dengan phpinfo()

we permitted to upgrade php library as we like, but i don know to to it

Thanks

Please help us.
www.silih.org
Environment Study base on Indonesia