Well, officially he's right - anything above 2GB (i.e. 4GB and up) should be SDHC, and needs to be supported by the device explicitly, and it often takes a firmware update. My camera got one, for example (Pentax *ist DS).
I haven't tried any 4GB cards, however, and (if
Wikipedia has it right) there are 4GB cards around that are not SDHC, nor strictly SD spec. So that may be why you had 4GB working. But with 8GB it's definitely SDHC all the way, and you'll have to try the manufacturers.
