I just installed gentoo. I have two nics (8139too and 3c509). I did: ifconfig eth0 192.168.1.2 (for 8139too). That worked fine. But for 3c509 nic, i tried to do ifconfig eth1 192.168.1.1. I got a "no device" for eth1. I did modprobe 3c509 and got an error message:
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/lib/modules/2.4.20-gentoo-r5/kernel/drivers/net/3c509.o: init_module: No such device
Hint: insmod errors can be caused by incorrect module parameters, including invalid IO or IRQ parameters.
You may find more information in syslog or the output from dmesg
/lib/modules/2.4.20-gentoo-r5/kernel/drivers/net/3c509.o: insmod /lib/modules/2.4.20-gentoo-r5/kernel/drivers/net/3c509.o failed
/lib/modules/2.4.20-gentoo-r5/kernel/drivers/net/3c509.o: insmod 3c509 failed
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is there any way to set the irq for this device by force?

One of the problems that may have something to do with this is that there is an onboard audio card (ac97). I installed a creative sound blaster card (ensoniq 1371). In the dmesg, the ac97 codecs are mentioned and so is the sound blaster card. Just not the 3c509 nic.