I am new to MAC OS X. Please help me with the following compiling error.

I have flex 2.5.4a and g++3.3 on my MAC OS X 10.3 machine. When I tried to compile my tool on the MAC
I got the following error:

In file included from /usr/include/FlexLexer.h:51,
from lex.yy.cc:237:
/usr/include/gcc/darwin/3.3/c++/backward/iostream.h:36: error: using
declaration `istream' introduced ambiguous type `istream'
lex.yy.cc: In member function `virtual int yyFlexLexer::yylex()':
lex.yy.cc:1245: error: cannot convert `std::istream*' to `istream*' in
lex.yy.cc:893: warning: label `find_rule' defined but not used
lex.yy.cc: In member function `void yyFlexLexer::yy_load_buffer_state()':
lex.yy.cc:1776: error: cannot convert `istream*' to `std::istream*' in
lex.yy.cc: In member function `void
yyFlexLexer::yy_init_buffer(yy_buffer_state*, std::istream*)':
lex.yy.cc:1827: error: cannot convert `std::istream*' to `istream*' in

Can anyone give me help? I know that g++2.95 can be compatible with flex, but for certain reason, I can not do that.