Shared_buffers and kernel parameters, tuning

After days of searching and testing I have come up with this way of
configuring our postgresql 7.2 db.
I have not yet increased my shared_buffer as high as suggested below on our
prod machine (24-7 high traffic), but after testing on our dev machines
this allows at least the databse to start up. It is very difficult to test
the actual performance since there is a hugh difference in traffic on dev
and prod.
Here is what we have:

We have a high traffic system with a database described as followed:

4 pentium 3 633 cpu's
3753456 kB RAM (3.5 Gb)
Red Hat Linux 7.2
postgresql 7.2

What I like to do is:

/proc/sys/kernel/sem=250 32000 100 500 (after advise from forum/docs)
/proc/sys/kernel/shmmax=1921769472 (RAM / 2 * 1024 - this
piece of math I got from some of oracle's support pages (ooopps) actually )

/proc/sys/kernel/shmall=1921769472 (RAM / 2 * 1024)

in postgresql.conf:

shared_buffers = 117248 (shmmax / 2 / 1024 / 8 ) This I got from this forum.

Does this sound right or am I totally out of bounds here? I have, as said
before done this on our dev macine ( a lot smaller machine ), but it would
be nice with some feedback ..

Thanx in advance for response.

/rune