How to install Ushahidi on dreamhost server

I heard a lot of people talk about Ushahidi, in official site said that The Ushahidi Platform is an open source web application for information collection, vizualisation and interactive mapping, it allows people to collect and share their own stories using various mediums such as SMS, Web Forms, Email or Twitter. so I try to install it on my Dreamhost hosting server. it is have iOS application, it is universal application means work well with iPhone/iPod/iPad once download.

go to http://download.ushahidi.com/ then download Ushahidi, unzip,  open readme.html file, check out Required Extensions, Dreamhost offer all of bellowing php extensions:

1. PCRE must be compiled with –enable-utf8 and –enable-unicode-properties for UTF-8 functions to work properly.
2. iconv is required for UTF-8 transliteration.
3. mcrypt is required for encryption.
4. SPL is required for several core libraries.
5. mbstring which speeds up Kohana’s UTF-8 functions.
6. MySQL which is required for database access.
7. IMAP which is required for email functionality.

and have to chmod bellow files to 777  ,make sure those folders writable,

chmod -R 777 application/config
chmod -R 777 application/cache
chmod -R 777 application/logs
chmod -R 777 media/uploads
chmod 777 .htaccess

last night I tried many times to install Ushahidi, I follow all instructions but still  failed , always show me “500 Internal Server Error” even go to http://[Your Ushahidi URL]/installer on on begin,

1. I try to remove .htaccess the I can finish installer process , but I can’t login to /ushahidi/admin
2. I try to change site_domain on config.php, always show me  Internal Server Error
3. I try to change index_page to index.php on config, Can’t login
4. I try to change RewriteBase /ushahidi/ to “RewriteBase /” on .htaccess, still show me  Internal Server Error
5. I try to comment “RewriteRule .* index.php/$0 [PT,L]” on .htaccess, show me Internal Server Error
6. I try to remove “RewriteRule .* index.php/$0 [PT,L]”  and add “RewriteRule ^(.+)$ index.php?kohana_uri=$1 [L]” on .htaccess, show me Internal server error
7. I try to download newest version from https://github.com/ushahidi/Ushahidi_Web ,it doesn’t work
8. I try to comment “Options +FollowSymlinks”, it is work!

I am beginner of Ushahidi and hope Ushahidi getting better,I hope someone from Ushahidi leave a message and tell me truth: why not put kohana_uri behind index.php?