hey, whats the advantage of using a 17" over 15". better picture quality, larger screen etc. ? or maybe even a 19". i want the largest projection size possible with excellent quality. what sizes approximately maximum should i get with a 15, 17, and 19 inch ? thanks

LCD size has nothing to do with the size of the projected image. The benefit of using a 17" screen is the increased resolution compared to a 15". Your standard 17" LCD has a resolution of 1280x1024 which covers the required 1280x720 pixels for true 720p high def content. 15" LCDs generally have resolution of 1024x768 which cannot display 720p.

As stated, one benefit is that 15" LCD have a 1024x768 resolution, while 17" & 19" LCD's have 1280x1024 resolution, which will lead to better picture quality. It appears that 17" LCD's are becoming the "standard" as prices drop and competition increases... what you will find is that most 17" LCD carry better specs in terms of their response times and contrast ratios, so generalizing based on specs, we'd say that 17" LCD's have better quality that way. (of course the true test of any LCD is by looking at it and see how you like the picture)

What size screen are you looking to make ? As a general guideline I would recommended the following:

15" LCD for max 90-100" screen
17" LCD for max 140-150" screen
19" LCD I wouldn't recommend as there are no benefits over a 17" LCD.
15.4" WUXGA LCD for 150"+ screens.

again, these are mostly my opinions, others may vary widely from these...

@tameone,
15" LCD's are capable of displaying 720p material by the use of a scaler, and it will look great. (esp. since 720p needs to be downscaled for it to be displayed on a 15")... just thought I would mention this...

cheers,
gs