IRQ conflict on ethernet cards

[Eric Smith <Eric.Smith@fruitcom.com>]

I have a RealTek and a 3com card which are both sharing the same irq
viz. /proc/interrups:

           CPU0       
  0:     899149          XT-PIC  timer
  1:      20820          XT-PIC  keyboard
  2:          0          XT-PIC  cascade
  6:        106          XT-PIC  floppy
  8:          1          XT-PIC  rtc
 10:          0          XT-PIC  eth0, eth1
 13:          1          XT-PIC  fpu
 14:      90746          XT-PIC  ide0
NMI:          0

Here is the grepped  /proc/ioports:
....
f800-f87f : eth1
fc80-fcff : eth0
....

and part of the dmesg:

3c59x.c 18Feb01 Donald Becker and others http://www.scyld.com/network/vortex.html
eth0: 3Com 3c905B Cyclone 100baseTx at 0xfc80,  00:50:04:11:f3:eb, IRQ 10
  8K byte-wide RAM 5:3 Rx:Tx split, autoselect/Autonegotiate interface.
  MII transceiver found at address 24, status 7849.
  Enabling bus-master transmits and whole-frame receives.
rtl8139.c:v1.07 5/6/99 Donald Becker http://cesdis.gsfc.nasa.gov/linux/drivers/rtl8139.html
eth1: RealTek RTL8139 Fast Ethernet at 0xf800, IRQ 10, 00:40:f4:2e:41:c8.
eth0: Initial media type Autonegotiate.
eth0: MII #24 status 7849, link partner capability 0000, setting half-duplex.

I can get both eth0 and eth1 to work (support a network connection)
strangely but not simultaneously, although modprobe only works on eth0
and not eth1.

I did all I could on the simplistic CMOS that I have but I cannot
allocate IRQ specifically to ports.  I also ran the reltek dos
diagnostics and setting utility and all is fine but I cannot 
change the IRQ from 10 with it.

How do I manually force the IRQ to be different on the two cards?

Thank you.

--
Eric Smith