German "umlaut insensitive" query

I want to query words with German "umlauts" (special characters) with
and without normalization. I want to find "grün" (green) written
"gruen" as well.

Using "LIKE" with locale de_DE.iso88591 does not help (Locale support
shoud affekt "LIKE",
http://www.postgresql.org/docs/7.3/static/charset.html#AEN21 761).

Any Idea how to solve this? Difine a special Operator? Has anyone
already done this before?

Using PostgreSQL 7.3.2 on Linux.

TIA,
Robert Strötgen. :)