you should install the pro*c compiler from the oracle cd.

Then you sould use the following command:
$ORACLE_HOME/bin/proc code=cpp sys_include=(...) include= (...) cpp_suffix=(...) char_map=STRING iname=...

sys_include = compiler and system specific includes (like /opt/SUNWspro/SC5.0/include/CC for Sun C++ compilter ver 5.0)
include = oracle include directories and your code include directories (see below)
cpp_suffix = the output of the proc (C/CPP)
iname = file name to compile

Oracle include directories:
$ORACLE_HOME/precomp/public$ORACLE_HOME/plsql/public,$ORACLE_HOME/network/public,$ORACLE_HOME/rdbms/demo,$ORACLE_HOME/rdbms/public

When you compile the c/cpp use these flags:
-I$ORACLE_HOME/precomp/public
-I$ORACLE_HOME/plsql/public
-I$ORACLE_HOME/rdbms/demo
-I$ORACLE_HOME/rdbms/public