Do most Linux distributions boot up and immediately recognize a USB keyboard/mouse? (That is, they work automatically without the need for any special boot parameters/options.)
If you have PS/2 ports, you should use those with your keyboard and mouse. Especially if the kb/m already have adapters for them. There is less to go wrong with the PS/2 ports than there is with USB. Some BIOSes will not recognize USB keyboards. If you have USB-to-PS/2 emulation available, and enabled in the BIOS, the USB keyboard will be translated to i8042 (PS/2) in hardware, and will appear to the BIOS, and whatever OS you load, as a standard keyboard. It is best though to physically use the PS/2 port for your PS/2-capable devices.
Actually, even that's not normally necessary. I've used some old Super 7 motherboards that required that be enabled to have the BIOS respond to the keyboard, but Linux could care less - it Just Worked. The only time when I've ever, ever found it necessary for Linux's operation to set the legacy BIOS options was when I was using an early kernel (2.4.x) and a new, somewhat eccentric keyboard that wasn't recognized. ( http://www.notestation.com/flex_keyboard.htm )
-Sean