Install a particular version of gcc.

 sudo apt-get install gcc-4.4  
 sudo apt-get install gcc-4.4-multilib  
 sudo apt-get install g++-4.4  
 sudo apt-get install g++-4.4-multilib  
 sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.4 60 --slave /usr/bin/g++ g++ /usr/bin/g++-4.4  

I am using ubuntu 12.04, and my default gcc version is 4.7. I wanted to install gcc 4.4.

 ~$ gcc -v  
 Using built-in specs.  
 Target: x86_64-linux-gnu  
 Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.4.7-1ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu  
 Thread model: posix  
 gcc version 4.4.7 (Ubuntu/Linaro 4.4.7-1ubuntu2)