you can edit the XML file with any unicode text editor (ie Notepad), but be warned - support may decide not to support you if they can't understand the error messages you are giving them.
What message do you want to change?
Thanks I will have a look.
Simon addressed this in another post: http://community.mcafee.com/message/5517#5517
You can edit the SBErrors.xml file but customizations will not display in pre-boot. They will display in Windows UI though...
It would be nice if this file could modify the default error messages pre-boot.