video & modem irq conflict- change IRQs?

I recently installed an NVIDIA geforce2 mx/mx400 agp video card in my computer. Device manager shows its sharing IRQ 11 with an onboard Advance AC’97 audio for VIA Audio controller and a Supramax 56i PCI v.90 modem. Often, not always, when the modemis used, (and sometimes when it isn’t), the computer suddenly reboots, losing anything I was doing. The support people at NVIDIA said move the modem to another IRQ. I haven’t been able to do that yet. The option isn’t available. I’m running Windows XP Pro, have tried changing the bios(Award v6.00PG, moving the modem to other PCI slots, to no avail. Any suggestions on changing IRQs, etc.?