I've tried every version of MGW from 0.67 to 0.69 (including yesterday's CVS snapshot) on SME 5.6 and it works great. Here's what I do for a quick and dirty install:
1) Create I-bay (w/ dynamic content)
2) Download and extract MGW to your hard drive (it will create a subfolder - "moregroupware" or "mgw" depending on what version you have)
3) Copy/move the files from the subfolder to your HTML folder in your I-bay
4) Login to your SME server as "root" and run "mysql"
5) Create the database:
create database mgw;
6) Grant permissions:
grant all privileges on mgw.* to mgw@localhost identified by 'your_password';
7) Point your browser to
http://www.your_domain.com/your_ibay/setup/index.php and follow the instructions from there...
I think that covers everything - I just did the above less than 12 hours ago, so it should still be fresh in my mind. It's not the most secure method of installing, but it's quick and easy. You can always go back and limit the database and file permissions, but it works quite well using the above process.