I don't think this is a software issue. SDHC
is not backwards-compatible with older SD card readers. New readers can recognize older cards, but not vice-versa. Unless the reader clearly states that it can handle SDHC, then it will probably never work.
For the record, I also have several devices that are unable to use SDHC cards, including my Sharp Zaurus. Fortunately, it also has a compact flash slot, so I can use an SD/CF adapter similar to this one
to read them.