Windows Updates and Device Drivers
If your version of XP is not fully up to date, you may have issues running certain applications, including games. Blizzard's Diablo support pages don't mention Windows XP, so there is no certainty of compatibility, even with a fully updated version of XP. Obsolete device drivers can also cause software issues. Check that your display adapter, sound card and CD-ROM are running the most current versions of their respective drivers.
Reinstall
A straightforward first step in dealing with a computer game problem is to completely uninstall the game. Next, restart your system and reinstall the game. Check that the game discs are clean and relatively scratch-free before inserting them into your CD-ROM drive. Also, ensure that no unnecessary background programs are running during the installation process. Overtaxing your hardware can potentially introduce errors during installation. Launch the game after it's installed and see if the crash problem persists.
Diablo Game Patches
Blizzard releases updates and patches to its library of games on a regular basis. These updates correct bugs that somehow made it past the testing phase and into the wide release version of the game. While patches for the original Diablo game went dormant long ago, it's still possible that your copy is not fully up to date. Navigate to Blizzard's Diablo page and check that the latest patch (1.09 as of the date of publication) matches your game version. If not, download and install the patch.
Insufficient Hardware
The graphics engine of Diablo is undemanding by the standards at the time of publication, but if your computer still runs XP, the game may be pushing your system to its design limits. Diablo's characters and environments move and change rapidly, demanding ample amounts of video memory. A dated video card, overloaded hard drive or bogged down processor could all contribute to games crashing or locking up. Check your computer's vital statics and compare them to the game's requirements. Update your hardware as necessary.