Just bought a 4GB Secure Digital card marked SDHC. I know this is the new standard for SD, but I expected that my iMac, less than one year old, would recognize the chip. My older HP Windows machine recognizes the 4GB SDHC card instantly, I can read and write on the Windows Vista machine. My iMac does not recognize the chip at all. Is this a general problem? Or is it unique to my machine?