Thanks for the reply Andrey..
Points in order:
1: The primary key error only happens if I click "Go Ahead!" a second time - obviously it's partially populated the DB already.
Using PHPMyAdmin I can empty and create new DB's, so I now have 2 test DBs, which I've been dropping all the tables from prior to each install.
So on a totally blank DB, I hit the install button and get this error returned:
Invalid bind-variable name ':title'
2: I can't seem to set the error log at the moment - not sure why that is, but can't get php to write to the log for now, but will try and get that sorted shortly.
3: I've added what you suggested to the .htaccess file, and it now looks like this:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^.*$ - [NC,L]
RewriteRule ^.*$ index.php [NC,L]
php_flag log_errors On
php_flag ignore_repeated_errors On
php_value error_log Z:\intranet\php\php_errors.log
Out of interest, my PHP Version is 5.4.13, and MySQL version is 5.6.10.1 on a Windows2008 R2 64bit server - has SEOTOASTER been tested with any of these, would it cause any problems?