I'm thinking this is the Windows "bug" where if there are enough read errors it will slow down the drive to PIO mode. Problem is that it doesn't tell you!!
I'm not sure if this is the correct way to fix this, but I would disable DMA for all your IDE channels (see link above). Then reboot. Then re-enable DMA for all channels and reboot again.
Another option is to install AnyDVD (sorry for the advertisement in this forum). Aside from removing copy protection, this program is a low level cdrom driver that, in addition to the bug described here, fixes other Windows cdrom quirks as well, such as the name of a CD/DVD not being displayed in Explorer when you insert a new disc in the drive.