Linux bridge thruput problem

If this isn't the right newsgroup for this, please let me know.

I have a P4 2.4GHz system with 4 3COM 3C905C cards installed, running 2.6.7
and Slackware 10 distrib.

The kernel is compiled with bridge support and ebtables support. I have the
brctl tools and ebtables tools installed

I have executed these commands:

brctl addbr port
brctl addif port eth1
brctl addif port eth2
brctl addif port eth3
ifconfig eth1 0.0.0.0
ifconfig eth2 0.0.0.0
ifconfig eth3 0.0.0.0
ifconfig port up

Note, eth0 is connected to a 10mbps broadband connection and is assigned an
IP. eth1 is connected to the same network. eth2 and eth3 have test
machines connected to them via. crossover cables.

Now, on this server, I can do Internet downloads at 800-900K/second - i.e.
the traffic goes via. eth0.

However, the test machines on eth2 and eth3 can only do Internet downloads
at 30K/second. It's like I have a bandwidth limiter installed, but of
course I don't.

Why is my bridge giving me such poor performance?

Paul Gani