Trying to get 2.3.0 working now...
I got a little further by doing as instructed per Sam. However, I am getting the the error below.
I have submitted a ticket for this to my host (reseller account). However, is there anything I can do to get past this?
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Installing SilverStripe...
I am now running through the installation steps (this should take about 30 seconds)

If you receive a fatal error, refresh this page to continue the installation

Creating 'mysite/_config.php' for use with _ss_environment.php...
Creating /home/aliyswor/public_html/mysite/_config.php
Creating '.htaccess' file...
Creating /home/aliyswor/public_html/.htaccess
Building database schema...
Checking that friendly URLs work...
Friendly URLs are not working. This is most likely because mod_rewrite isn't configuredcorrectly on your site. Please check the following things in your Apache configuration; you may need to get your web host or server administrator to do this for you:
mod_rewrite is enabled
AllowOverride All is set for your directory

@ Froshi: I had same error: Fatal error: SS_DATABASE_PASSWORD must be defined in your _ss_environment.php.
and it was simply due because PHP tags was missed: <?PHP ?> in _ss_environnement.php file.
It should solve the issue.

Just had the same issue because I was following the instructions "to the T". Adding the tags got me back. Thanks, Jonas.

The same issue.... No solution?

Well, the fix for me was as jonas posted. Just add the <?php tag. Somehow, I'd forgotten it because I didn't see it mentioned in the instructions.