Where and how can I download g++3.2 if have gcc4.1.2 to compile an old code?

Please try from the below site

http://rpm.pbone.net/

If your linux is RPMs based then you can simply download using YUM
Issue the following command

yum install gcc

The above should work on CentOS, Redhat (if you have enabled subscription).  It also requires YUM repository to be properly setup.
If you have CD/DVD for your Linux, it may already have it and you can simply install it from it.

This is what I get:

[root@pet1 pluginconf.d]# yum install gcc
Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
http://download.fedora.redhat.com/pub/fedora/linux/extras/6/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404: Date: Thu, 03 Mar 2011 16:24:52 GMT
Server: Apache/2.2.15 (Red Hat)
Content-Length: 343
Content-Type: text/html; charset=iso-8859-1

Trying other mirror.
Error: Cannot open/read repomd.xml file for repository: extras

Hi,

I have g++3.2 already downloaded it but I don't know how to install it. I was told that I need to install with gcc3.4 but not sure how..

I downloaded it in /usr/local  directory and I do the following:

./configure  ;which works fine

make  ; but I get the following error message
[root@pet1 gcc-3.2]# make
make[1]: Entering directory `/usr/local/gcc-3.2/libiberty'
rm -f needed-list; touch needed-list; \
        for f in atexit calloc memchr memcmp memcpy memmove memset rename strchr strerror strncmp strrchr strstr strtol strtoul tmpnam vfprintf vprintf vfork waitpid bcmp bcopy bzero; do \
          for g in mkstemps.o ; do \
            case "$g" in \
              *$f*) echo $g >> needed-list ;; \
            esac; \
          done; \
        done
echo regex.o cplus-dem.o cp-demangle.o md5.o alloca.o argv.o choose-temp.o concat.o dyn-string.o fdmatch.o fibheap.o floatformat.o fnmatch.o getopt.o getopt1.o getpwd.o getruntime.o hashtab.o hex.o lbasename.o make-temp-file.o objalloc.o obstack.o partition.o pexecute.o safe-ctype.o sort.o spaces.o splay-tree.o strerror.o strsignal.o ternary.o xatexit.o xexit.o xmalloc.o xmemdup.o xstrdup.o xstrerror.o > required-list
make[2]: Entering directory `/usr/local/gcc-3.2/libiberty/testsuite'
make[2]: Nothing to be done for `all'.
make[2]: Leaving directory `/usr/local/gcc-3.2/libiberty/testsuite'
make[1]: Leaving directory `/usr/local/gcc-3.2/libiberty'
make[1]: Entering directory `/usr/local/gcc-3.2/zlib'
true "AR_FLAGS=rc" "CC_FOR_BUILD=gcc" "CFLAGS=-g -O2" "CXXFLAGS=-g -O2" "CFLAGS_FOR_BUILD=" "CFLAGS_FOR_TARGET=-g -O2" "INSTALL=/bin/sh /usr/local/gcc-3.2/install-sh -c" "INSTALL_DATA=/bin/sh /usr/local/gcc-3.2/install-sh -c -m 644" "INSTALL_PROGRAM=/bin/sh /usr/local/gcc-3.2/install-sh -c " "INSTALL_SCRIPT=/bin/sh /usr/local/gcc-3.2/install-sh -c" "LDFLAGS=" "LIBCFLAGS=-g -O2" "LIBCFLAGS_FOR_TARGET=-g -O2" "MAKE=make" "MAKEINFO=makeinfo  " "PICFLAG=" "PICFLAG_FOR_TARGET=" "SHELL=/bin/sh" "EXPECT=expect" "RUNTEST=runtest" "RUNTESTFLAGS=" "exec_prefix=/usr/local" "infodir=/usr/local/info" "libdir=/usr/local/lib" "prefix=/usr/local" "tooldir=/usr/local/x86_64-unknown-linux-gnu" "AR=ar" "AS=as" "CC=gcc" "CXX=c++" "LD=ld" "LIBCFLAGS=-g -O2" "NM=nm" "PICFLAG=" "RANLIB=ranlib" "DESTDIR=" DO=all multi-do
make[1]: Leaving directory `/usr/local/gcc-3.2/zlib'
make[1]: Entering directory `/usr/local/gcc-3.2/fastjar'
make[1]: Leaving directory `/usr/local/gcc-3.2/fastjar'
make[1]: Entering directory `/usr/local/gcc-3.2/gcc'
HEADERS="auto-host.h ansidecl.h  i386/biarch64.h i386/i386.h i386/att.h dbxelf.h elfos.h svr4.h linux.h                  i386/x86-64.h i386/linux64.h defaults.h" DEFINES="POSIX" \
        TARGET_CPU_DEFAULT="TARGET_CPU_DEFAULT_athlon_sse" \
        /bin/sh ./mkconfig.sh config.h
config.h is unchanged
HEADERS="auto-host.h ansidecl.h  i386/biarch64.h i386/i386.h i386/att.h dbxelf.h elfos.h svr4.h linux.h                  i386/x86-64.h i386/linux64.h defaults.h" DEFINES="POSIX" \
        TARGET_CPU_DEFAULT="TARGET_CPU_DEFAULT_athlon_sse" \
        /bin/sh ./mkconfig.sh hconfig.h
hconfig.h is unchanged
gcc -c -DIN_GCC    -g -O2 -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wtraditional -pedantic -Wno-long-long  -DHAVE_CONFIG_H -DGENERATOR_FILE    -I. -I. -I. -I./. -I./config -I./../include ./read-rtl.c -o read-rtl.o
In file included from ./read-rtl.c:24:
./rtl.h:125: warning: type of bit-field âcodeâ is a GCC extension
./rtl.h:128: warning: type of bit-field âmodeâ is a GCC extension
./read-rtl.c: In function âfatal_with_file_and_lineâ:
./read-rtl.c:62: warning: traditional C rejects ISO C style function definitions
./read-rtl.c: In function âread_rtxâ:
./read-rtl.c:662: error: invalid lvalue in increment
make[1]: *** [read-rtl.o] Error 1
make[1]: Leaving directory `/usr/local/gcc-3.2/gcc'
make: *** [all-gcc] Error 2

You need to type make bootstrap to build gcc from source. I don't think bootstrap is the default target.

Very helpful