The thing about the guestbook is, it's not a feature of MSN Spaces, it's a cunning use of the blog and list features.

Basically, do the following:

• Create a blog entry called: Guestbook
• In that entry, put a message of your own creation asking people to leave a message.
• Publish the blog entry
• Preview your space
• Click on 'Permalink' at the bottom of the Guestbook blog entry.
• Copy the link for later use.
• Create a new custom list called: Guestbook
• Add one entry to the list called: Leave a message (or something similar to that).
• Set the link for that entry to be the permalink of your blog entry called guestbook that you copied earlier.
• Customize your space and place the list called Guestbook wherever you want.
• To start with your Guestbook blog entry will be on your front page, but as you add blog entries it'll become hidden and all you're left with is a list that links directly to it. Bob's your uncle!