There are already some great resources out there! Take a look:
Geekfeminism has some specific suggestions for creating a welcoming environment for women (and all conference-goers) http://geekfeminism.wikia.com/wiki/Women-friendly_events
They've also posted a sample code of conduct for events that will help set an inclusive tone for your event, http://geekfeminism.wikia.com/wiki/Event_Guidelines
Dec.2010 update - some recent incidents have sparked the creation of an Anti-Harassment policy for FLOSS events, http://geekfeminism.wikia.com/index.php?title=Conference_anti-harassment_policy