Before attempting an upgrade to XP, run the free Microsoft Upgrade Advisor.
It will run many minutes, then tell you what hardware and/or software is
incompatible with XP. If hardware, either replace, or possibly do a BIOS
flash (if available). If software, remove, get an XP-compatible version,
the re-install after XP is up and running. nOte that all CD software, virus
software, system-like software (e.g., Norton) should be removed BEFORE
upgrading. Even if the box says XP-compatible, these software load
different DLLs for XP than for older systems, so they must be un-installed
then re-installed.
Then, unplug all periperals, except for the monitor, mouse, and keyboard.
This includes any USB devices and/or hubs.
Run SCANDISK and verify that ther are no errors, or fix them.
Defrag, then run SCANDISK again.
Be sure that you have at least 2 Gig free, preferrable more.
Backup all personal files, just in case !
Now, try the upgrade.
If that fails, try a clean install, which will first format the hard drive.
(See note on backup above.)