They make up to a 16gb micro sd,
I believe they have the drivers on here or at xda-developers.com,
all you have to do is install those drivers
and your device will be able to use anything up to a 16gb micro sd card,
I believe they are working on a 32gb micro sd card,
but I don't believe that it is out on the market yet.
driver is located at:
http://rapidshare.com/files/207700754/SDHC.zip
(I downloaded from xda and reuploaded it to my premium account)
Instructions from xda post:
"once downloaded put on your ppc and install the .cab file, small file (31kb)"