NFS Gateway - German special characters

Hello,

we work with NFS Gateway for NetWare 6.5 since a few weeks.
Our problem is: Users created filenames with german special characters like
"ä" on the linux filesystem (SLES9). On their Windows-workstations the
filenames on the volumes (mounted through NFS Gateway) contains wrong
characters instead of german special characters.
Are there any ideas to solve this problem?

Many thanks in advance,
Andreas