Just before I posted this I discovered the answer but it may help others.
I have installed the presentation tool on my test elgg installation and, apart from a few browser issues noted elsewhere, it works as expected. So, I thought I was ready to install it on my live site. I used svn to install it, made the .htaccess changes and the database changes were successful.
However, when using Safari it worked but when using Firefox i got the "white screen". The error in the log was about memory being exhaused so I increased the php.ini setting to 32M and restarted apache. However, still got the same problem. Then I noticed that the new elgg (0.8) htaccess file set the php memory limit itself to 16M. I commented this out and then it all worked again.
So, if you have access to your php.ini file and usually make changes there remember to comment out this line from the elgg htaccess file:
php_value memory_limit 16777216
If you don't have access to the php.ini file and get the "white screen of death" try upping this memory limit.
Keywords: memory, presentation