Hmm, your IRQ isn't changing?  I think XP is overriding your BIOS IRQs.
Try uninstalling the sound card and enable your onboard sound once again.  List your IRQs again so we can see if your onboard is also IRQ16.
Also, when flying online, right click on the map and select I think it's "net status".  Does your variance spike when you press the "T" key?  Does your connection show any delay in the network?  Another possibility is it may have something to do with your network card...
Wing, I am thinking it's either
1)IRQ conflict
2)network card issue
3)or something to do with your Microsoft UAA Bus Driver for High Definition Audio.
Will know once you gather more info.
Sorry to bother you but also check to see if your preferred recording device and tell us what's it's selected to.
BTW, good luck in FSO. 
I was able to get the sound card on IRQ18 by moving some fans around.
IRQ 0   System timer   OK
IRQ 4   Communications Port (COM1)   OK
IRQ 5   Intel(R) ICH10 Family SMBus Controller - 3A30   OK
IRQ 6   Standard floppy disk controller   OK
IRQ 8   System CMOS/real time clock   OK
IRQ 9   Microsoft ACPI-Compliant System   OK
IRQ 13   Numeric data processor   OK
IRQ 16   Intel(R) 4 Series Chipset PCI Express Root Port - 2E21   OK
IRQ 16   ATI Radeon HD 4800 Series   OK
IRQ 16   Intel(R) ICH10 Family USB Universal Host Controller - 3A37   OK
IRQ 16   Standard Dual Channel PCI IDE Controller   OK
IRQ 16   Intel(R) ICH10 Family PCI Express Root Port 6 - 3A4A   OK
IRQ 17   Microsoft UAA Bus Driver for High Definition Audio   OK
IRQ 17   Intel(R) ICH10 Family PCI Express Root Port 1 - 3A40   OK
IRQ 17   Intel(R) ICH10 Family PCI Express Root Port 5 - 3A48   OK
IRQ 17   Marvell Yukon 88E8056 PCI-E Gigabit Ethernet Controller   OK
IRQ 18   Intel(R) ICH10 Family USB Universal Host Controller - 3A39   OK
IRQ 18   Intel(R) ICH10 Family USB Enhanced Host Controller - 3A3C   OK
IRQ 18   Intel(R) ICH10 Family PCI Express Root Port 3 - 3A44   OK
IRQ 18   Creative SB X-Fi   OK
IRQ 18   Intel(R) ICH10 Family USB Universal Host Controller - 3A36   OK
IRQ 18   Marvell Yukon 88E8001/8003/8010 PCI Gigabit Ethernet Controller   OK
IRQ 19   Intel(R) ICH10 Family USB Universal Host Controller - 3A35   OK
IRQ 19   OHCI Compliant IEEE 1394 Host Controller   OK
IRQ 19   Intel(R) ICH10 Family 4 port Serial ATA Storage Controller 1 - 3A20   OK
IRQ 19   Intel(R) ICH10 Family 2 port Serial ATA Storage Controller 2 - 3A26   OK
IRQ 21   Intel(R) ICH10 Family USB Universal Host Controller - 3A38   OK
IRQ 23   Intel(R) ICH10 Family USB Universal Host Controller - 3A34   OK
IRQ 23   Intel(R) ICH10 Family USB Enhanced Host Controller - 3A3A   OK
I updated to SP3 and have all the updates to date.
Net status    No spikes when hitting the vox buttons.
Preferred recording device is SB X-Fi Audio [001]
Still have the screen freezes