tg3 and Interrupt storms

Hi everyone,
I'm currently using a gentoo box as a gateway for a LAN to manage
traffic shaping and other small tasks. It's configured as follows:
- kernel 2.6.12.5
- dual Xeon, 1GB ram
- two Broadcom BCM57xx gigaeth cards, for the internal and external
networks
- tc and iptables are used, with quite simple rules
- no other application is running on this box

Using ipconfig/iptraf I see a lot of IP crc errors, and it seems to be
impossible to exceed 30-40Mbps between the two ethernet, even if the
load is around 0.01

With vmstat i can see a huge numer of interrupts:

procs -----------memory---------- ---swap-- -----io---- --system--
----cpu----
(...)
0 0 2560 117820 817436 14408 0 0 0 0 9903 32 0
1 99 0
0 0 2560 117820 817436 14408 0 0 0 0 9167 30 0
1 99 0
(...)

Is there anything I can do with tg3 module to avoid this situation and
enhance the performances?

Thanks for the help