i think it HAS TO BE 2G only
That's not necessarily correct. It has to be a regular SD card, it can't be SDHC. They do make 4 GB SD cards, but its not likely that you'll easily find one. Chances are, this 4 GB SD card is SDHC.
So yeah, you're basically capped at 2GB unless you can find a 4 GB SD that isn't SDHC.