Lowering the speed is unlikely to solve your errors, try unloading all of your USER called TSRs from memory, hit CTRL+ALT+DEL (if you have winxp or 2k) and close down unneccesary processes. Also shut off things that access your HDD, such as screensavers, IRC (when writing logs), filesharing apps and anything else. That may help you out.
If you are trying to burn something with copyright protection, or burning an ISO that was downloaded, you may have errors with the actual ISO that aren't jiving with it's Table of Contents.
Try a different burning software, you never know what might work better.