Thanks to Scott I've found out about MS SharedView - which allows you to share your screen with up to 15 users. Currently in beta 2 and free, you can download it here.
"Connect with up to 15 people in different locations and get your point across by showing them what's on your screen. Share, review, and update documents with multiple people in real time.A Windows Live ID (Passport, Hotmail, or MSN) is required to start sessions, but not to join sessions. New in Beta2: now even easier to use, with group chat and performance improvements!"