BuddyPress.org

i had a similar issue, this is how i fixed it.

htaccess on root directory:

# BEGIN WordPress

<IfModule mod_rewrite.c>

RewriteEngine On

RewriteBase /

RewriteCond %{REQUEST_FILENAME} !-f

RewriteCond %{REQUEST_FILENAME} !-d

RewriteRule . /index.php [L]

</IfModule>

# END WordPress

permalink structure:

/index.php/%postname%/

then i had to make sure that apache has the mod_rewrite module enabled.

running wordpress 2.9.2, apache 2.2.11 and php 5