It means something is wrong. Have you uninstalled the Via 4-in-1 driver and gone back to the Microsoft IDE driver yet? If so, then it suggests a problem with the transfer mode negotiation between the IDE controller on your motherboard and the PX-712A. It is also possible that the transfer mode is not being reported correctly.
Check to make sure the IDE channel your PX-712A is attached to is using the proper legacy resources. For primary IDE channel, you should see IRQ 14 listed in the resources tab, IRQ 15 for secondary IDE channel.
If the PX-712A is attached to the secondary IDE channel, you can try uninstalling this channel within the WinXP device manager, and rebooting to allow WinXP to PnP it again. You can then check to see if the transfer mode goes back to UDMA mode 2 or persists in UDMA mode 4.
I am guessing it is possible for PlexTools to have compatibility problems with certain chipsets in certain IDE resource configurations. You can try updating PlexTools to the latest 2.15 without your PX-712A attached (since you get a BSOD), shut down, then reattach the PX-712A to see if things get better.