The newest Ubuntu (10.10) has gcc version 4.4.4, but I need 4.2.1 for compilation issues. The library that I'm using requires me to use 4.2.1.
How can I downgrade the gcc to a specific version?
You can't really downgrade gcc. However, if you don't need 4.2.1 specifically, but 4.2.x, you can install Ubuntu 8.04 which will continue to have the