I was just running into this same issue on a TI TravelMate 5000 laptop, where I also could not find PCMSS.exe.
I think the installer is supposed to identify what PCMCIA controller you have, and rename one of the various exe's included with the installer to PCMSS.exe, but either it's broken or doesn't exactly match one of your controllers.
In my case, the installer found I had a Cirrus Logic controller, so I guessed either PCMSSCL9.exe or PCMSSCL2.exe was the one I needed. I just ran them from the DOS prompt, and in my case PCMSSCL2.exe didn't complain, so I copied it and renamed it PCMSS.exe.
After that, all the rest of the drivers worked fine and it was able to identify the CompactFlash adapter card. In my case, though, the system would lock up when I tried to access it. I found a setting in the BIOS called "PCMCIA Resources", and I changed it from its default "Minimum" to "Maximum" and the card started working great. A nice way to get files on and off this laptop with no CD drive!
People Can't Memorize Computer Industry Acronyms