Miguel, this may have many causes, so please clarify:
1. Does low fps happen only when it rains in game or your character is among many trees? Trees and rain contain lots of 3d data, so the card might be overloaded.
2. Do you get decent fps in other graphics-intensive games like Warsow or Nexuiz? If no, your system is too slow.
3. Have you installed the proprietary nVidia drivers instead of nouveau? Check this by typing in terminal 'dpkg -l nvidia-current' (note: this works only for Debian, Ubuntu, and Mint). If there is 'ii' in the beginning of the line, the driver is installed.
4. Do you have a dual video card, eg. nVidia Optimus? If so, EL may be using Intel card instead of your GeForce. To check this, type in terminal 'lsmod | grep nvidia'. If 'nvidia' is not listed, try forcing nVidia use with optirun.
Hope it helps.
