XDA-Developers forum provides a patch for Windows Mobile 5 and 6 Pocket PC devices that allows you to read and write data to and from Secure Digital (SD) storage cards that are larger than 2GB.

SD High-Capacity (SDHC) card provides more removable storage capacity range starting at 4GB and going up to 32GB. SDHC features three speed classes - Class 2, Class 4 and Class 6 - allowing transfer of data at least 2, 4 and 6MB per second respectively. Because SDHC cards work differently than standard Secure Digital memory cards, this new format is not backwards compatible with legacy SD format host devices.

Visit this thread to download a compatible version of SDHC patch for your make and model of Windows Mobile device.