i am new to the build ur own projector and i want to know if i need a widescreen lcd to display 16:9 images onto the projector screen or not

any assistance would help

If you're driving it with a PC, usually not. Most widescreen monitors aren't natively 16:9 anyway. It might save a bit of depth in your box if you get a widescreen monitor but a standard 17" 1280x1024 (which is actually 5:4) will probably be cheaper.

No, if you have a 4:3 or a 5:4 monitor and want to say watch hdtv or play xbox 360, something that is in HD, it will cut off the top and the bottom to make it a 16:9 image. Or you can buy a scaler or some transcoders such as a Viewsonic N6, which will give you the option of displaying images in either a 4:3 or a 16:9 aspect ratio. If you watch alot of HD content then it might be better to go with a widescreen monitor because a widescreen will give you a true 720p or 1080i picture rather than a streched out image from a 4:3 or 5:4.
Hope this helped!

Different monitors will act in different ways.

If the 17" LCD is "HD Ready" then it will display a 16:9 formatted signal correctly: either by centering the image (to maintain a 1:1 pixel ratio) or by streching or shrinking the image while maintaining the aspect ratio to fill as much of the screen as possible. This means that with an "HD Ready" monitor: HD content, Xbox360, etc. will look right.

Keep in mind that widescreen monitors can also strech or shrink a 4:3 image to fit as well.