Although all mainboards are forced to do something similar, they are all a bit different. However, the first PCI slot almost always shares with the AGP slot. I've never seen anything different.
My KA7-100 only leaves 2 and 4 with their own IRQ's. 3 shrares with USB, and I think 5 and 6 share with each other. Something like that.
Check your mainboard manual or the FAQ for your board for details. Also, be sure to disable any onboard devices you don't use to free up the extra IRQ's. I've done this by going to USB devices allowing me to disable the PS/2 port, serial ports, use a network printer so I disabled the printer port... etc. Disable everything you can to free up those IRQs!
