Hi, if you are experiencing complete hangs with programs, which result in locked up system, as Kirk said, Windows XP generally shields well itself from the programs so they shouldn't crash completely the system.
Common cause for hanging with high system load (which, loading hundreds of photos in PM or Capture NX can be) is either aging, bad or badly seated memory, or overheating of components on the motherboard/cpu.
I suggest, if the issues persist, that you try to run memtest (memtest.org) and cpuburnin (separately, with nothing else running, perhaps in safemode), these two programs test the memory and cpu for errors which are common when things are going bad. The reasons for this could be either bad memory (which commonly exhibits itself only under heavy load such as graphics programs which do a lot of writes/reads to memory), badly seated memory, hot cpu, badly seated cpu. Or even a bad power supply which fluctuates when the cpu draws too much power (ie running at 100%). Or something system-level such as old graphics card driver.
I have quite a few times mysterious problems when running system intensive programs which I later traced to bad cpu cooler.
Hope this helps, Frantisek