The graph looks just like one from another member with a DELL PC.
-Go into BIOS and make sure both IDE channels are set to AUTO detect and that the NEC is seen by the BIOS. Is it running in DMA mode 2?
-Reboot and go into DEVICE MANAGER and remove the IDE CHANNEL that's connected to the NEC. Reboot and windows will reload driver. Check to see that the NEC is running in DMA mode 2. If you have more than one optical drive connected to the IDE, then set the jumper on both to Cable Select.
-Defrag both hard drives. Download HDTUNE and run/post your transfer speed.
-Burn a DVD at 4X and monitor the CPU load under Task Manager during the burn. Does it hit 90+%.