I'm experiencing an annoying problem with my USB controller. Short story: My USB won't work when I have network, audiocard and Nvidia installed simultaneuosly.

My system:

ASUS a7v333-x motherboard ACPI BIOS rev 1004
AMD Athlon(TM) XP 1700+
Nvidia Geforce MX 420
ASUSTek/Broadcom 440x 10/100 Integrated controller
Realtek AC'97 Audio for VIA (R) Audio controller

IRQ 0 System timer OK
IRQ 1 Standard 101/102-Key or Microsoft Natural PS/2 Keyboard OK
IRQ 6 Standard floppy disk controller OK
IRQ 8 System CMOS/real time clock OK
IRQ 9 Microsoft ACPI-Compliant System OK
IRQ 12 PS/2 Compatible Mouse OK
IRQ 13 Numeric data processor OK
IRQ 14 Primary IDE Channel OK
IRQ 15 Secondary IDE Channel OK
IRQ 16 NVIDIA GeForce4 MX 420 (Microsoft Corporation) OK
IRQ 18 ASUSTeK/Broadcom 440x 10/100 Integrated Controller OK
IRQ 21 VIA Rev 5 or later USB Universal Host Controller OK
IRQ 21 VIA Rev 5 or later USB Universal Host Controller OK
IRQ 21 VIA Rev 5 or later USB Universal Host Controller OK
IRQ 21 VIA USB Enhanced Host Controller OK
IRQ 22 Realtek AC'97 Audio for VIA (R) Audio Controller OK

Here's what I did to try to fix the problem:

Upgraded BIOS and did some tweaking according to
http://www.usbman.com/Troubleshooter%20General.htm#BIOS

Reinstalled winXP w/SP2 integrated and my USB devices works fine.

But when network, Nvidia and Audiocard is installed the USB device drivers disappear from device manager, and I'm not able to reinstall. I've rolled back to fresh XPSP2 install and tried to install the network etc. drivers in different orders, but to no avail. When all 3 are installed - no USB. I then tried to install them with drivers from asus, windows update, nvidia, gainward etc, but got the same result. When I disable one of the drivers and reboot my USB is working again.

Also tried the VIA USB2.0 260-L drivers from viaarena.com

Can I rule out an IRQ conflict? Is that even possible in XP?
Is the VT6206 USB2.0 chip acting up?

I've been at this for one week now, and I'm about to give up. Any suggestions?

irq conflict

Hope this is better than nothing