problem upgrading to PostgreSQL 7.4

I was working with PostgreSQL 7.3.4 easily.
Yesterday I decided to made an upgrade to PostgreSQL 7.4.2.
After upgrading from internet with the setup.exe I followed the normal
procedure to inicializate the postgre. Observe that The initdb failed.

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admin@alejo ~
$ ipc-daemon &
[1] 935405

admin@alejo ~
$ initdb -D /usr/share/postgresql/data
The files belonging to this database system will be owned by user "admin".
This user must also own the server process.

The database cluster will be initialized with locale C.

creating directory /usr/share/postgresql/data... ok
creating directory /usr/share/postgresql/data/base... ok
creating directory /usr/share/postgresql/data/global... ok
creating directory /usr/share/postgresql/data/pg_xlog... ok
creating directory /usr/share/postgresql/data/pg_clog... ok
selecting default max_connections... 10
selecting default shared_buffers... 50
creating configuration files... ok
creating template1 database in /usr/share/postgresql/data/base/1... FATAL:
could not create shared memory segment: Function not implemented
DETAIL:  Failed system call was shmget(key=1, size=1081344, 03600).

initdb: failed
initdb: removing data directory "/usr/share/postgresql/data"

admin@alejo ~

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My questions are:
a) Why I get the FATAL error if I have started the ipc daemon before the
initdb?
b) How to fix this?

Note.- This is no the first upgrade I made. The upgrading from version 7.2
to 7.3 was without problem.

I'll appreciate any answer