the system boots with no problem, but crashes or freezes when certain applications are run

It may seem as if the application is corrupt,but try a diagnostic such as AMIDIAG from AMI or Tufftest from windsor technologies
WWW.TUFFTEST.COM

Run repetive test on the cpu.While cpu run in real mode, diagnostics can detect errors running protected mode instrustions and perform through register checking.AMIDIAG stands out here because of the very specific error codes that are returned.Not only will tell you if the CPU checks bad, but it will also tell you the specific reason why.
  When an error code is returned suggesting a CPU fault, try another CPU.If a CPU fault is not detected, expand the diagnostic to test other portions of the motherboard.If the entire system checks properly, you may indeed have a corrupt file in your application.

The system boots with no problem, but crashes or freezes after several minutes of operation, the system BIOS mis-identifiers the proccessor, An older system refushes to run properly when the cpu's internal, the p4 or Athlon XP speed is reported incorrectly...more wait for that