Hokay So. Since someone said they were unable to play Postal 2, I decided to give it a go. I have the 10th Anniversary version fwiw.
1. Mount the CD.
2. From the cd run ./linux_installer.sh --target (insert directory here). This will extract the installer's files to the target dir.
3. In the target dir edit setup.sh and on line 267 remove the "2" from setup.gtk2. Source
4. Run setup.sh.
This installed the game for me. I was able to run it and get into the game, but I had no sound.
To fix sound I had to install alsa-oss and then run it as aoss ./postal2. Now it works as intended. Source
This worked for me on Ubuntu 10.10 32-bit.