Watch this screencast for a step by step walk through on how to sign up for a Microsoft Online Services and BPOS trial account.  It will only take about five minutes to watch this BPOS screencast.  The actual sign up process is slightly longer end to end when you will actually go to start it yourself.  Here are some initial steps to follow.

1. Sign up for a BPOS trial by clicking the link.
2. Create a new Live ID by following the Sign Up link on the page that appears.
3. Sign in with the Live ID you just created and request a BPOS trial.
4. Log into the hotmail account associated with the Live ID you created and wait for three e-mails, the final of which is the confirmation e-mail you'll click through and log into the Administration Center for Microsoft Online Services.