Sometimes yes, sometimes no, it seems to depend on the system. This is why having a spare PS/2 keyboard around isn't a bad idea, unless you have a somewhat newer Dell without any USB ports, in which case you get to call Dell and complain to them if things don't work.
I apologize in advance if this is a silly question, but I need to reinstall Windows XP on my Dell Dimension 8400 and I only have a wireless keyboard and mouse (receiver uses a USB port). Will I run into trouble? I have heard that there may be an issue because of the device drivers. Any input would be greatly appreciated.