AFAIK, Xilinx never made PAL and GAL chips. I have always used AMD's PalASM, which produces GAL Jedec files if you choose "PALCE16V8" as the chip type.
PalAsm is a DOS software and does NOT run properly in the DOS window of win9x or Win2k. When AMD sold it's programmable logic division to Lattice, they did not continue the software.
I have lost my copy of PalAsm in a harddrive crash about a year ago, but I might have an old AMD developer CD with a copy of MachXL and PalAsm.
The Commodore people used Cupl if I remember right - just to give you some keywords to search in file sharing networks.
Prepare to use an old DOS machine, because the chip is totally outdated. If you want to enter the world of programmable logic, you might want to look into the 8BitBaby - a high-quality prototyping board with connectors for four popular 8-bit computers and a socket for a 64-macrocell CPLD by Altera (8 times the capacity of the 16V8 chip). No need for a programmer, because the chip is in-system-programmable.
good luck,
Jens Schönfeld