Having problem with initdb on my Solaris 8 box

I am new to PostgreSQL. I downloaded PostgreSQL 7.1.3 and followed
instruction to ./configure, gmake, and gmake install. gmake told me
that I successfully made PostgreSQL and ready for installation. After
I installed, I could not get it started. I went back and did gmake
check. I got an error message which saved in initdb.log. Here it is:

   The program
       '/usr/local/pgsql/bin/postgres'
   needed by initdb does not belong to PostgreSQL version 7.1.3, or
   there may be a configuration problem.

When I checked postgres --version, I got v7.1.3.

I am confussed. Can someone give me some hints?

Thanks!

Paul