The size just depends on the price you're willing to pay. The 19" with the same specs as a 17" will obviously be 'better' if you can pay for it.
Some things to consider:
- Look for a display with a good response time: the best ones are currently at 12ms. The lower the response time, the less the 'ghosting' on the screen when there are rapid changes.
- Look for a decent contrast ratio and brightness
- Since you're planning to watch movies/DVDs on this thing, it might be a good idea to look for a widescreen (16:10) display instead of a regular on (4:3)
I agree a good response time is vital, most gamming sites recomment 16ms. since he mentioned not playing games something a bit slower will be fine...........just get a 19 samsung, they are not that expensive or try from BenQ.