In order for you to play Team Fortress 2 on Linux with minimal graphics settings, your computer must meet the following requirements
Operating System:
Ubuntu 12.04
Processor (CPU):
Dual core from Intel or AMD at 2.8 GHz
Memory (RAM):
1 GB RAM
Graphics Card:
nVidia GeForce 8600/9600GT, ATI/AMD Radeon HD2600/3600 (Graphic Drivers: nVidia 310, AMD 12.11), OpenGL 2.1
Network:
Broadband Internet connection
Storage:
15 GB available space
Sound Card:
OpenAL Compatible Sound Card