There is no need to create a user on your XP machine since NASLite doesn’t care who you are. It simply assigns the same user to everyone. The reason you are having problems with NASLite is that your windows machine locks files for use and then fails to unlock them. That is not common, but may occur with some applications that tend to be sloppy with the filesystem and leave without cleaning after themselves.
In order to verify, reboot XP and connect to NASLite via FTP using IE or equivalent. See if you can kill the problem files that way. I assume that the only problems you are having is with the app that you described in the earlier post. If that is the case then the above acessment is in fact correct.
Hope that helps.