I finally got around to trying the diva distribution of OpenSim. I followed the instructions available here, which actually weren't as complicated as it seemed at first glance. So long as you follow it step by step then it's pretty fool-proof. Although I've had previous experience with both OpenSim and an equivalent of MoWeS called XAMP, so I'd be interested to hear about other people's experiences.
One step that did look as though it could be a lot simpler was the setup of the MySQL server. My recommendation would be that at the point when you're choosing Apache2, MySQL5 etc in the MoWeS mixer (pretty much the first step in the instructions), that you also select PHPMyAdmin in the Application software section.
In step 1, after you get confirmation that Apache and MySQL is running, open a web browser and go to: http://localhost/phpmyadmin/
In the window that opens click on the Privileges tab (shown as 1 in the image).
Enter a User name of opensim, set a password (including retyping it), as shown in 2. Then select the radio button option to create a database with the same name, as shown in 3. That's it. No use of command prompts or typing in unfamiliar strings of text.
I've only had a brief play so far, but I'm looking forward to trying out the web interface and sending things flying around the Megaregion. My only concern was that I couldn't connect to it from another PC. Whether this is due to permissions or the hard-coded local IP I don't know. Hopefully the former.