I know I had this problem with S2 Fots always crashing to desktop because I run win 7 32 bit. Looking at forums I see Im not the only one. Some of you may of also had to same problem with Empire total war when it first came out. Well its the same solution!
I did not come up with this solution!
It was given to me by creative assembly when I posted my problems in the Support thread.
http://www.twcenter.net/forums/showthread.php?t=238484
It may say for Empire Total war but It works for Shogun 2, its what I had to do and now I can play! Fallow the instructions here its really simple and has alot of information on the subject of Virtual Memory.
This is not a fix just something you can do till one is made.
Enjoy =)