[link|http://www.ifixit.com/iPhone-Parts/iPhone-1st-Gen|These are all the parts] that are available for purchase for the 1st generation iPhone.
As Alex mentioned, the 3G digitizer is not compatible with the 1st generation. Further complicating things, the [guide|449|opening procedure] for the phone is very difficult, so you should definitely read through the guide before attempting to replace the display assembly.