As I understand it, there are some hacks to allow SD cards to appear to be bigger by tweaking block size or something like that. However, that means that they are flouting the standard. SDHC specifically allows sizes greater than 2GB, but that doesn't mean that your card is an SDHC card. More likely it's one of the not-quite-SD cards.
That said, I just got the
SanDisk ImageMate 5-in-1 reader (link likely to break, since they managed to misspell their own company name in the URL and in the description) that claims to support SDHC. It seems reasonably fast for the cards I've tried it with, although I'm not really an expert on such things.