I think the advantage of digital projection is you need only to carry a laptop which nowadays can weigh as low as 2 lbs and yet can carry more than 5000 pictures. Imagine dragging 5000 slides around and the hassles of loading them. A protable digital projector weighs about the same or slightly less than a slide projector but is less bulky and so also easier to carry around.
Using a laptop you can integrate your lecture and slide show with software like Powerpoint and this may allow you to lecture better and your photos to demonstrate your point better ( may be that is why it is called Powerpoint)
For those who sell photos another great advantage is if your client doesn't like your image you can tweak your photo to his liking on the spot with your laptop. Showing your client the process of tweaking and your willingness to tweak to suit his taste will probably help you to sell more photos. But then you need a bigger and faster laptop so your client doesn't have to sit and wait for too long.
So with all these advantages even though the quality may not be on par with the old slide show ( but then may not be that far you if you have a good setup) I think digital projection still has a lot to go for.
I think for projection of photos you don't need 16:9 ratio projector. The best portable projector available today should be a 1280*1024 DLP projector. DLP projector gives much better contrast than LCD ones and a better black. But if you are presentng in an illuminated room then you may still need a grey screen, like a Stewart Firehawk which will give you better black and contrast. Most portable projectors can manage 2000 or more Lux and so room darkness is not such a great problem.
There are many slide projecting softwares which will take care of the resolution issue and you don't have to worry too much about this. My suggestion is you keep two copies of each photo on your hard disk. The original RAW file and a jpeg file at 1280*1024. The jpeg file is for presentation in a slide show. Anything bigger than your projector's native resolution is a waste of space ( you have a bigger file) and time ( your computer has to downsize your file before the projection). The RAW file is for in case your client or student asks to see more details or you need to tweak the photo on site. The combined size would be about 10 MB and so you can easily carry 5000 photos on a 80 G hard disk and still have load of space for your OS, photoshop, RAW processing software and whatever else you need or fancy.
But before you jump into all these one thing you must make sure is that you know or can get somone to calibrate your projector ( and of course the monitors of your laptop and your desktop at home, and your printer if you are going to sell prints). Calibration is a BIG issue in the digital world. Without proper calibration your photos taken with great expertise and loving care may be presented in totally wrong color and dynamics. if you are really new to the game may be a Mac is a better choice than PC because Mac has better support for ICC profiles and so in case you cannot have custumn profiles created for your gears you can just use the profiles that the manufacturer supplies and you cannot be that far wrong.
You can give me an email -
if you need more advice on your digital setup ( actually it is all the way from your camera to your projector ) and I will be willing to help. It is not that complicated and yet not that simple either for a transformation from film to digital. But after you have gone through the hard part you will find that you are in a totally new world and you will wonder why it takes you so long to change.
