This is from the Steam forums but due to the amount of positive feedback I assume this will work.
I've just set this up on my 2 computers, here's the steps I took:
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Nvidia
Right click Nvidia icon in tray and select Nvidia Control Panel
Choose Manage 3D settings from list on left
Go to Program settings tab
Press "Add" and browse to ...Steam\steamapps\common\aliens vs predator demo\avp.exe
Maximum pre-rendered frames - click where it says Use global setting(3) and change it to 1
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ATI
Go to http://downloads.guru3d.com/download.php?det=733 and hit Download Now
Install the Tray Tools (run as administrator in Vista/7, and turn off UAC when installing)
Go to the new Tray Tools icon in the tray (it's a red and white diamond), right click and choose Game Profiles
Set Profile Name ("AvP demo" would be a good choice)
Executable - browse to ...Steam\steamapps\common\aliens vs predator demo\avp.exe
"Set 3D to" <- tick this box, choose Custom Settings from the dropdown box and press Edit.
Go to the "3D Additional" tab, in the Flip Queue Size dropdown box select 1
Press OK.
Now back in the Manage Game Profiles window, press the save button (looks like a floppy disk) at the bottom under profiles.
Press Close
Done
I know Jippy was having this issue, I wasnt so I cant do a personal test to be sure. If you were trying this and posting here to confirm would be very helpful. Also, this could be an issue thats a glitch that will be fixed in the final product, keep in mind the demo build is from 10 monthes ago.
I've just set this up on my 2 computers, here's the steps I took:
________________________________
Nvidia
Right click Nvidia icon in tray and select Nvidia Control Panel
Choose Manage 3D settings from list on left
Go to Program settings tab
Press "Add" and browse to ...Steam\steamapps\common\aliens vs predator demo\avp.exe
Maximum pre-rendered frames - click where it says Use global setting(3) and change it to 1
_______________________________________
ATI
Go to http://downloads.guru3d.com/download.php?det=733 and hit Download Now
Install the Tray Tools (run as administrator in Vista/7, and turn off UAC when installing)
Go to the new Tray Tools icon in the tray (it's a red and white diamond), right click and choose Game Profiles
Set Profile Name ("AvP demo" would be a good choice)
Executable - browse to ...Steam\steamapps\common\aliens vs predator demo\avp.exe
"Set 3D to" <- tick this box, choose Custom Settings from the dropdown box and press Edit.
Go to the "3D Additional" tab, in the Flip Queue Size dropdown box select 1
Press OK.
Now back in the Manage Game Profiles window, press the save button (looks like a floppy disk) at the bottom under profiles.
Press Close
Done
I know Jippy was having this issue, I wasnt so I cant do a personal test to be sure. If you were trying this and posting here to confirm would be very helpful. Also, this could be an issue thats a glitch that will be fixed in the final product, keep in mind the demo build is from 10 monthes ago.