If you're trying out xTuples Postbooks on F15 64 bit you may need to install some extra libraries because of errors thrown during install:
"There has been an error.
/opt/xTuple/postgresql/bin/initdb: error while loading shared libraries: [libkrb5.so.3|libaudit.so.0]: cannot open shared object file: No such file or directory
The application will exit now."
# need these installed
yum install audit-libs.i686 krb5-libs-1.9.1-5.fc15.i686
# however libaudit still throws a problem so I symlinked as follows
ln -sf /lib/libaudit.so.1 /lib/libaudit.so.0
Thanks! I was having the same problem in CentOS 6 i686, however audit was already installed. The symlink cleared it right up.