Thought I'd share this in case anyone is using Bluehost and trying to get Omeka up and running.
I had lots of difficulties, and it took a few rounds with tech. support to find someone who could nail down the issue. Once found, it seemed to be all good. Here's a run-down.
1. Though they're on PHP 5.2, their configuration doesn't have pdo_mysql active. That needs to be done in the php.ini file in all directories. Start with the php.ini file they provide in the root directory and add this under the list of extensions.
extension=pdo.so
extension=pdo_mysql.so
Make sure you copy the php.ini file into all the subdirectories
2. I'm fuzzier about this one--maybe someone in the forum with deeper knowledge of Apache can help me out. They said that the php_value command in the .htacces file needs to be moved into the php.ini file. Their tech. support did this for me and all is good, but I didn't think ahead enough to ask them for a line # to see what exactly they did--bad and silly me.
Without those, I was getting errors that php_value was not defined, couldn't be found, or couldn't be initialized. I would also get this Apache error: [an error occurred while processing this directive].
Upshot: if you're using bluehost, these are some things to watch for. And, don't let their tech. support go in circles by telling you repeatedly to make sure php.ini is copied into all the directories. Ask about the php_value command in .htaccess that needs to be moved to php.ini.
Good luck!