postgres.h

Hi,
I'm trying to compile and run some external functions on postgres. The code
seems to compile and run fine on linux machine. But on cygwin, it gave me
errors saying it couldn't find some files such as "postgres.h",
"server/executor/executor.h", "server/executor/spi.h"

Could someone please tell me where to find these files. My
/usr/include/postgresql/ only includes 1 folder called internal. I checked
google for these files and it seems they should be in a folder
../postgresql/server
But I don't see that in my directories. I have postgresql 7.3.4 installed.

Thanks,
Nupur