Hi anybody reading this. I've worked this out myself (solution: can't have a php.ini in the root of my web site), but in the spirit of hopefully helping anyone else who might come across this in their own servers, here's what happened to me.
At the time of this problem, my specific version is 2012062504.01 (2.3.4+ Build: 20130118).
I have moved from a sub-folder on a test box to a dedicated vps with cpanel. after some confusing with the host getting php 5.3.x installed (they seem to default to 5.2 still for some paranoid reason), managed to get moodle showing up.
I had to ensure that the moodledata folder had the correct permissions (0777).
I tried setting my sessions to file-side (rather than db-side, as is the default in moodle 2). I did this by adding
$CFG-> dbsessions = "0";
to my config.php (this has now been removed again as the site is running). This post was helpful in determining if the site was actually running (watching sessions get created, confirming that it was taling to the db, etc).
My .htaccess file looks like this (with strips www off the front, since it's redundant):
# Use PHP 5.3
# AddType application/x-httpd-php53 .php
RewriteEngine on
RewriteCond %{HTTP_HOST} ^www\.mydomain\.com$ [NC]
RewriteRule ^(.*)$ http://mydomain.com/$1 [R=301,L]
My problem appears to be that the host has added a php.ini file to the root folder.
AcceptPathInfo
cgi.fix_pathinfo=1
I'm not sure what these lines do, and there's all sorts of posts related to Moodle that assure that one host requires them and another does not in order to get Moodle to play ball. I tried changing my (entire) php.ini file to this:
post_max_size = 100M
upload_max_filesize = 100M
but that did not help. Also, my host has chosen the absurd default upload limit of 2MB, hence my attempt to change them, so I guess I won't be uploading my 120MB scorm packages after all...
Anyway, as stated earlier, my ONLY solution so far is to remove the entire php.ini file (even if it is empty, moodle is still breaking)
It would be nice if someone could explain a possible reason for this in a reply, as a quick google reveals that it's a common enough problem that stumps a lot of people.