I usually spend 15 minutes before a presentation trying to get the television to talk to my notebook over the chained HDMI/DisplayPort dongles. Sometimes it never works.
Here's a solution that is compact, portable, and involves a minimum of cables to get your notebook presentation AirPlaying over a wireless network to any HDMI capable device.
Buy an AirPlay capable Apple TV, HDMI cable, and the new Airport Express that looks like a white version of the Apple TV. Costs $200 and looks cute together.
One time setup
Configure Airport Express to get its WAN configuration via DHCP (you won't need this for AirPlay) and act as a DHCP-NAT service. Have the Apple TV connect to the Airport and turn on AirPlay. Connect your laptop to the Airport, too. Now everything is configured to work in the Airport's private network.
In the meeting room, power both devices, connect the television to the Apple TV. Connect your computer to the Airport network and AirPlay your desktop to the television.
Start your presentation =)