Anything over 2gb is SDHC. If you're seeing cards that are 4gb that don't say SDHC they're typos. SDHC is a new technology that is actually not compatible with any device older than 2007.
It stands for secure digital high capacity. It's not just a bigger card, it's read different. So again, anything over 2gb is SDHC no matter what the packaging says.