I used to backup my home folder to a CD-RW or a DVD-RW by dragging it to the new CD icon in OS X 10.4 without a hitch. However, after the upgrade to OS X 10.6 the burning always failed with the message 'could not open the data fork of <unable to get file path> (-43).' resulting in an unusable disc.
The offending file turned out to be ~/Library/Preferences/com.apple.sideebarlists.plist. It appears that the Finder modifies this file while burning the disc. The solution was simple: lock the file (check the lock check-box in the Get Info window obtained by right-clicking the file and selecting Get Info) before burning.
There might be some side effects to locking this file (such as being unable to modify the sidebar) so you could unlock the after burning the disc.
This is clearly an OS X 10.6 issue: I have reproduced the problem by doing a clean install on an external drive and booting from that fresh install and burning the freshly created user home folder located on that drive.
[crarko adds: I haven't tested this one.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20100710033106328