Cannot change IRQ settings

I am having problems trying to figure out how to manually change the IRQ settings in the Windows 2000 Pro, and XP Pro final release. All of my hard ware is stuck at IRQ #3. I believe this is causing my system to slow down. I have tried to change thesettings in the mainboard bios but the OS just changes the IRQ setting to another all sharing IRQ! In the OS itself all the edit buttons are greyed out.
I would really apprecate it if someone would take the time to explain to me where I can find the setting that will allow me to edit my IRQ’s manually.
(What is being shared is :
both on board USB ports, the on board sound, my AGP video card, my network card,and the ACPI.

Thank you.