There’s a note on the Windows Vista Team Blog about a…
New compatibility update for SD cards
…for large (8GB or more) SD cards and improved support for SDHC and SDIO cards. I bought my first 4GB SDHC cards last week and was surprised to find that none of my older SD card readers (including the one built into my desktop) could read it. Fortunately, Sandisk included their MicroMate SDHC card reader with the card itself. I’ll test it with a Vista desktop as soon as the update becomes available on the 22nd.