When starting ISE 9.1i or 9.2i on a RHEL 3 or RHEL 4 machine it will hang or freeze on the splash screen and nothing will happen. If the execution is aborted there will still be a $Xilinx\bin\lin\_pn process running, but it will be using 0% of the cpu.
This was reported by a customer and resolved by deleting the $XILINX/.qt/.xilinxrc.lock file.
Make sure the _pn process isn't running and then delete the .xilinxrc.lock file. Once this is deleted try launching ISE again and it should work as normal.
Note: This resolution hasn't been verified, if anyone is able to reproduce the issue and verify the solution please let me know so we can publish this AR externally.