1.8ghz ssd 1st gen
Can it play 720p and can it also display it to 24" lcd
It can, but make sure you have all of the software updates installed. It will run hot and begin to stutter over time if you play videos for a long period of time. It also get's really hot if you connect it to an external display but is capable of doing it. I have the same model you are talking about and have been using it since March, so I feel safe in giving you my opinion on it. The early 08 model Air is not a good laptop for video imo.
Now the late 08 Air I upgraded to could almost be a desktop replacement. It is the machine the first Air should have been.