Computers can crash for reasons unrelated to the operating system. Known hardware issues include:
1) overclocked CPU
2) overheated CPU
3) insufficient installed memory
The list of software issues is legion, and I cannot begin to advise you regarding this. That said, I recommend the following before you commence a serious hardware investigation:
1) Backup data files to external HD or USB flash drive.
2) Run Files and Settings Transfer Wizard, and save this invaluable folder to ext HD or USB flash drive.
3) Format the HD (NTFS).
4) Do a [i]clean[/i] install of XP SP2.
5) Reinstall applications.
6) Restore data files.
7) Run the Files Settings Transfer Wizard in reverse to restore your OS configuration.
8) Install and run [b]CCleaner[/b] (free):
http://www.ccleaner.com/
9) Install and run [b]Defraggler[/b] (free):
http://www.defraggler.com/
10) Save this HD configuration as an [i]image[/i] to an external HD with Norton Ghost:
http://www.symantec.com/norton/products/overview.jsp?pcid=br&pvid=ghost14
11) Install XP SP3.
If this works, problem resolved. If your system still crashes with XP SP3, you can recover the [i]image[/i] from backup using the Ghost disk, recovering your HD in <20 minutes (Ghost overwrites the HD at 1-2GB/min).
Good luck.
Rick/Portland, OR