shared_buffers and shmmax what are the max recommended values?

Hi all,
We have a web app that is using a 32 bit 8.1.4 (I know but upgrading
is not an option for another couple of months...) running on Suse 10.
We just increased from 3GO to 6GO of RAM, and I increased the various
memory related values...

First info - the server ONLY does one pg db (that is its purpose in
life, and it runs pretty much nothing else, and certainly nothing we
care about, all the apps that access it are on separate servers).

I did, however, realise that I don't (didn't?) understand what shmmax
REALLY is. It was at the default value (:-)), so even for 3GO was
ridiculously low. I saw some recommendations on the list mentioning
that shared_buffers (for an 8GO machine) should be set to 250000 or
something like that. So I merrily increased shmmax to 128MO and tried
to start pg. Ouch! I needed to put it to much more than that...

So the main question - what is the maximum recommended shmmax setting?
I currently have it set to 1GO, but I think it probably needs to go
higher - no?

Here are the values that aren't at their defaults:

shared_buffers = 50000
work_mem = 8192
effective_cache_size = 525000
max_prepared_transactions = 100
maintenance_work_mem = 262144

max_fsm_pages = 300000
max_fsm_relations = 10000

Any suggestions most welcome.
Cheers
Anton