How much memory in 32 bits Architecture to Shared Buffers is Possible

Hi, to all!

Recently i try increasing the memory values of shared buffers on one
IBM xseries 255 (Quad XEON 2.8, 8 GB RAM, 2 disk SCSI 36 GB(Raid 1), 1
Storage.

I try change these shared memory values to use 25% of memory ram (2048
MB) and effective_cache_size to 50% (4096 MB) of memory. All this
settings to 220 Max Connections.

Where I start up the cluster very messages of configurations errors on
shared_memmory and SHMMAX look up. I try change the values of
shared_memory, max_connections and effective_cache_size and large the
size of SHMALL and SHMMAX to use 4294967296 (4096 MB) but the cluster
don't start.

Only with 15% of value on shared memory i can start up this cluster.
In my tests the maximum value who i can put is 1.9 GB, more of this
the cluster don't start.

Can anybody help me and explicate if exist one limit to memory on 32
bits Architecture.

Anybody was experience with tuning servers with this configurations
and increasing ?

thanks to all.

--
Marcelo Costa