A dummy file is normally a large file that is added to an image to allow the disc to be read far easier becuase it pushes all the other data towards the outer edge of the disc. If you cant get something to boot on a crappy disc drive use new cd media This is not a new technique and was used with dreamcast homebrew apps to stop the wear of the laser motor, and give better boot times. CD Burning software normally burns the data alphabetically, so if you call the large dummy/fluffer file "1.bin", the rest of the data will be puched to the outside. To make dummy files, you can find a large file on your disk and rename it to an 'early' letter in the alphabet, or you can use a tool that will just generate a massive bin file of garbage to a setsize. I prefer the second method as you can set the perfect size for the dummy file and push all the data to the very edge, getting maximum compatibility and boot times.
On this page are some dummy file tools originally designed for the dreamcast, but can be used for the xbox:http://www.megagames.com/dc/dc_utils_disk.shtml
Personally i prefer DummyFile.exe as it is small and perfect for the jobhttp://www.megagames.com/console/cgi-bin/d...mmyfile!zip
This wont cure your cd boot problems, but it sure optimises the boot and reliability. If you want best compatibility of burnt discs check out some other faq's with guides for pot tweaking (last resort!!) and the best types of media to use