okay here is the deal i have the same problem and worked it out with potco team.
#1- make sure u have 2gb memmory or more with vista, vista is memmory hog if u have less then 2gb u are in a bog.
#2- if its your videocard wich was the problem for me is that, you probably have the newest drivers ... wich normally would not be a bad thing.. actually it would be the best thing... except for potco. you will need to downgrade your drivers to about 2006, most vid card support dont have downgraded drivers. so you will have to contact there customer support.
If your videocard is spanking new... then you need another one :P sorry
#3- is your settings try agressive conservation for memmory and lowest graphics that the game allows (this makes game slowwww as snails for me) but it works for others.
#4- being your game_options.txt file wich needs to be changed in combonation with your driver downgrades but sometimes works by fixing it onits own.
replace the content of that file with excatly as follows.
version
state
api
THATS IT!
it will re ajust it to your videocard... GOOD LUCK!
Dead bodies