I don't know about CycloDS , but i've got a 8GB Sandisk (class 4) in my DSTT and it works flawless.
Does it means, that the SD adapter which comes with the kingston SDHC wont work if I put it in my SD reader?Maybe it's just that your reader doesn't support SDHC?
I just got a 4gig Kingston Class 4 card but I haven't received my cycloDS yet. The thing that troubles me is that my computer can't read the 4gig microsd so now I'm afraid that my cyclods might not be able to read it either.