It might be. Quite a few things won't read the SDHC cards. I'd consider looking for a card reader, maybe one that fits in a drive bay (floppy or cd) if you don't want anything external.
You might try a different card reader as SNGX1275 suggests. I think cards up to 2GB store in FAT16 format. It seems that a computer should be able to deal with up to FAT32 at least with XP as the OS.