"I've downloaded the latest g++ and libg++ and I'm trying to install them on Linux, and I'm having lots of problems."
FSF releases of libg++ won't install on Linux unchanged, since Linux uses are part of the libio library from libg++ for its standard C library, only this is changed in a way that it clashes with libg++. This means that you'll need a patched version of libg++ for it to work.
If you want to upgrade to a new gcc/libg++ combination, the easiest thing to do is to grab the prebuilt versions of gcc and libg++ for Linux from `ftp://tsx-11.mit.edu/pub/linux/packages/GCC'. Follow the directions carefully. If you want to build from source, you'll need a patch for libg++; the Linux developers have named the patched libg++ version libg++-2.7.1.3 and there is a patch file in the above-named directory.
See `ftp://www.mrc-apu.cam.ac.uk/pub/linux/GCC-FAQ.html', the Linux GCC FAQ (though it may be a bit out of date; the Linux community moves quickly).