Just get a lock for your luggage -- the only downside to this is that if they think your bag has a bomb in it for some reason, they'll have to cut it apart . Screeners at some airports had been rifling through unlocked bags grabbing digital cameras, etc. before they were loaded onto planes, but I think once word got out the TSA has been watching them like hawks. I wouldn't put anything too fragile in a checked bag, though, unless it's wrapped in bubble wrap or the like and placed in a small cardboard box. I'd hate to have a hard disk not work afterwards because they dropped it, or a RAM module get cracked during handling.
Going through an X-ray scanner won't hurt a thing in your computer. Solid-state electronics are remarkably immune to most EM radiation, unless it is *very* powerful (like an EMP) or capable of causing residual radiation (which will ruin RAM chips by making some of the bits occasionally flip at random during operation). Hard disks are magnetic, and thus only affected by magnetic fields, not X-rays. But even a metal detector wouldn't be enough to scramble the bits on the disk platters -- the casing is magnetically shielded.