In order for you to play Team Fortress Classic on Linux with minimal graphics settings, your computer must meet the following requirements
Minimum: Linux Ubuntu 12.04, Dual-core from Intel or AMD at 2.8 GHz, 1GB Memory, nVidia GeForce 8600/9600GT, ATI/AMD Radeaon HD2600/3600 (Graphic Drivers: nVidia 310, AMD 12.11), OpenGL 2.1, 4GB Hard Drive Space, OpenAL Compatible Sound Card