If you install ModelSim (for example the free Altera Edition) on your 64-bit linux machine, you will miss some 32-bit libraries. On most systems, you can easily install them using either YUM or APT:
sudo yum install libXft.i686
sudo yum install ncurses.i686
See also
- Using the util package from Modelsim with VHDL 2008 (blog post)
- Tricking your Mac in to Believing it can run ModelSim (blog post)
- Is Xilinx slowly dumping Modelsim? (opinion)