Nothing in the tutorial of codeingniter for htaccess works for me. can anyone give me a hand?

[eluser]spidy[/eluser]
I am getting frustrated trying to figure out the issue of htaccess. I tried all the tutorial from codeingiter nothing is work.
I am running apache2 in ubuntu 10.04. the rewrite mode is already enabled.

Here is the url that I test.
———works————-
http://192.168.1.1/
http://192.168.1.1/index.php
http://192.168.1.1/index.php/blog
http://192.168.1.1/index.php/blog/comment

———Fail to work———-
http://192.168.1.1/blog
http://192.168.1.1/blog/comment

error that I get is error 404 page not found
the default error 404 from browser not from codeigniter

Greatly appreciate your help.