Sometimes when drives act up like that they've gone bad. Being the speed you listed, I'll guess the drives at least a couple years old.
You may ask, why does it work ok in DOS and not in Windows? First off, drivers are different for each and how Windows accesses the device is different than how DOS will address the device.
There is good news though. New CD-RWs are faster and cheaper than ever. Depending on where you live, TDK's 481628B which is an excellent performer can be had for about $70.00 after rebates. What you save in time and bad backups will probably eventually pay for the drive.
If you are completely unwilling to consider replacing the drive, you may want to fully try reinstalling Windows using the format option. My guess is that if you've reinstalled Windows already that won't fix it though (but I assume you have another CD device that enabled Windows reinstallation).