R4 doesn't support SDHC, at least the original one doesn't. I believe they came out with an updated version which does though.
its not an "offical" update, it was some other people (NOT the R4 team) that made it. there was always those 4gb SD cards (not SDHC) but i herd they sucked cuz of slow speeds and lag. im not even sure if they make 4gb SD cards anymore