Just to confirm. There are no restrictions on a user name. PC should have to handle anything LDAP throws at it.
Not 100% sure, but I wouldn't use any non-ASCII characters, neither for the user ID itself nor for passwords. Honestly I haven't tried it myself, but user names or password with e.g. German Umlauts may cause trouble in particular if the Windows PC running the client tools doesn't run in a code page which contains those German Umlauts (such as a Cyrillic Windows code page).