This is most often the case with new hardware (e.g. SCSI adapters or video/sound cards) where drivers for these boards haven't yet been written for the Linux kernel. It's usually only a matter of a few months before somebody on the net will contribute a driver for the hardware and support will appear in one of the almost weekly kernel releases. Care should be taken though when installing the Linux system if you're in fact installing a new distribution that may include something like ELF binaries which may not be supported by IRAF itself. Kernel updates can be done independent of a full installation which is the best route to add support for new hardware.
If you have a clone board for something like a sound card (which IRAF won't use) or SCSI adapter that isn't a true clone you can also run into problems. For these situations consult the net for advice on what can be used as a workaround, in some cases there will be no workaround so the best advice for new hardware purchases is to research or use only "standard" components in your hardware.