tightvnc make error: "Cannot find -lXtst"

[jet.eureka]

Dear friends:
    I encounted a make error when compiling tightvnc( unix version 4.0) in 
RedHat Linux 9.
    Following is the compiling output section which may reflect where I am 
trapped:
       ...
       c++ -O2 -Wall -o xOvncserver Image.o xOvncserver.o buildtime.o ..
       zlib/libz.a -lXtst -lXext -lX11
       /usr/bin/ld: cannot find -lXtst
       collect2: ld returned 1 exit status
       make[1]: ***[xOvncserver] Error 1
       make[1]: Leaving director '/home/jet/vnc-4.0-unixsrc/xOvncserver'
       make: ***[all] Error 1

   I am cofused by all these,and I appreciate it very much if anyone can
help me .
   Thanks for reading it.