There are 2 issues to be considered when moving to SDHC Cards:
1. Limitations of the SDHC cards with certain applications
There is no official SFC upgrade for the use of SDHC cards in the Loox Series. The commonly used driver is by "GreateVK & FreePK"
This driver works well with all my 45 proggies. The only limitation is that some programs can fail after being suspended. (Navigon MN6, Destinator, Skype) The program freezes and a restart become necessary. I’m not sure whether this is due to a shortcoming of the driver or a general limitation of the SDHC standard.
If you load the SDHC driver it will be installed into the memory of the device (not flashed to the ROM). You will lose this driver when resetting the loox. Your SDHC card will not be readable after a hard reset. Therefore you need to keep a small (standard) SD card with the installable SDHC Card Driver to prime the device after reset and make use of your SDHC card e.g. with backup files.
For someone with fair/good IT knowledge there is a better - but also somewhat riskier way. A Russian site offers free (experimental) software allowing flashing the ROM completely new. The WM6.0 version 038 that Newplowe created already comprises the SDHC driver – with the same limitation. Besides many other advantages with this version no Standard SD card has to be kept: The SDHC card is directly readable after a hard reset. But be warned, you can lose the PDA when doing something wrong while flashing, and of course the warranty will be void.
Hope this sheds some light...