samba - Jul 2005 - diaeresis _ not usable in the filenames in the samba home shares of windows XP clients

Hello,

my samba home shares [homes] are not correctly working for me.
I can not create a filename with _ character inside the name in my windows 
xp client homedrive. This must be possible under windows.
That must be something to do with the unix/samba charset.
Do somebody have an idea?

Best regards and many thanks
Andreas