I was told elsewhere that this file is found in the package Xfree86. I downloaded and ran the package. However, when I reboot it seems that X-windows gets damaged. I cannot see anything (just a blank screen) and cannot login to Linux
libXp.so.6 is a file found in Redhat Enterprise Linux 4. What I did was to copy the file and paste it in Redhat Enterprise Linux 5. I think the path was /usr/X11R6/lib. Oh yeah, you'll also have to place the path in your cshrc file.
If you install a newer or older RPM, your system could be damaged.
If you copy an older run time library to your system, you may need to set the environment variable LD_LIBRARY_PATH.