Originally Posted by Mountain 
The OS is 'Genuine Windows Vista® Home Premium - English'. It can be upgraded to 'Genuine Windows Vista® Ultimate (32Bit) - English' for £70 aswell.
Ultimate offers no real benefits to the average home user/gamer. Unless theres a specific feature of Ultimate you want, then its just £70 down the drain.
The 4Gb upgrade for me is a worthy selection and will work with 32bit, although you would be much better off with 64bit Vista, try speaking to a Dell sales rep and asking about 64bit OSs