I need the gcc -2.96 instead of gcc-2.3.. because of my requirement.if i downgrade the gcc did it effect on my sytem working. If yes Please help me how i was able to install both package.
thank you

Why do you require the earlier version of gcc? You could install both versions, but it may be better to find a way to use the newer version.

I need to install gcc for requirement which is supported by only this version of gcc.I have latest version when i try on new version it shows error So please help me how i will be able to install this version.

What software are you trying to compile that requires the earlier version? What error message do you get?

It's not uncommon for some software to require compilation by the same version used to compile the kernel. If this is the error you are having, it's probably best to recompile your kernel using the newer version.

If you do downgrade, I would use 2.95.3 - 2.96 is an experimental gcc that was buggy to say the least.
It has a history of miscompiling. You could also get 2.95.3 and compile it and install it to something like
/opt/gcc-2.95.3. this way, if you want to use gcc-2.95 just change your path to find that one first like:

export PATH=/opt/gcc-2.95.3/bin:$PATH

If you do use this way, when you install it don't forget to make a symlink for cc:

ln -s /opt/gcc-2.95.3/bin/gcc /opt/gcc-2.95.3/bin/cc

NOTE: If you downgrade gcc from say an 3.x to a 2.x you will probably break things on your system c++ related (mozilla/firefox, kde, etc...) hence the reasong for installing an earlier version in /opt and leaving the original gcc alone.