WinXP has a bug which they consider a feature. See DMA Mode for ATA/ATAPI Devices in Windows XP
. If more than six DMA errors are received, WinXP will turn off DMA and revert to PIO mode 4. High speed transfers using PIO 4 are very inefficient and have very high CPU utilization due to the lack of DMA (Direct Memory Access).
The symptom you have described is consistent with this WinXP "feature". You may have originally checked the settings and confirmed that DMA was enabled, only to find later that it has been reset to PIO mode without user intervention.
This is the most likely cause of your problem. If this is the case, the usual temporary fix is to uninstall the ATAPI device from Device Manager and reboot. When the burner is redetected, usually DMA will be reenabled.
If Device Manager continues to show DMA as enabled, the high CPU utilization indicates that something is probably interfering with the proper implementation of DMA and it is still not working. In this case I would double check the system BIOS for the proper DMA settings. Auto-detect is usually preferable, but if the problem continues with this setting try changing to a forced UDMA setting if available.
If UDMA worked OK before the most recent VIA drivers were installed, try an earlier version of the drivers.