SD cards I've got a Sandisk 2gb SD card for my NV3 and it's been working fine, now i've just bought 2 brand new Transcend SD cards both 4gb and when inserted into the camera it tells me that the memory is full. Any suggestions as to why?

Do the 4GB Cards say SDHC on them? They should. SDHC is simply "Secure Digital High Capacity". They're high capacity SD cards that hold more than regular cards. In this case, 4GB. The problem with these is that they need to be supported by the device. I've never put an SDHC card into a device that doesn't support them, but it looks like that's what your situation is. The highest memory capacity a non-SDHC compliant device is capable of 2GB. I recommend that you return the 4GB cards and buy 2GB cards instead.