I think your particular trade off will be between the "write and give presentations" and the "no more than 1/2 pound". The Viliv S5 is around 400 gms but it will handle everything else if you can accept the on screen keyboard. The UMID M1 adds back in the keyboard and gets down to almost 300 gms but I understand there are problems hooking it up to an external display. I can't speak for the N900. I understand it is handling Office files with Documents to Go. Unfortunately, Dataviz has not announced this and while they support editing presentations on some hardware they don't on others. It's also possible OpenOffice or one of its variants will work. Once you've got the presentation, the question would be could the N900 output it to a VGA/DVI/HDMI cable for projection.