Andy:
1- go to
http://seiv.pbw.cc/
2- Select graphics or text, according to your preference and your browser.
3- From here you'll have to find a "create account" button. In graphics mode, you'll probably find that its one of the SEIV icons along the top. (They're not just there for decoration=-)
Sorry I can't be more specific, but my browser logs me in automatically whenever I go to the site, so the "new account" controls aren't displayed to me.
It's pretty straightforward, all you need to give is a valid email address. It won't get spammed.
Once you have an account and are logged in, you can create new games or join existing ones quite easily.