How do I get 64-bit Vista?

I have a brand new Optiplex that came with Vista Ultimate and 4GB of memory.   Before I ordered the machine, I called and asked about the OEM Vista license because I knew that 64bit is required to access more than 3GB of memory and that the Retail Vista Ultimate License includes keys for both versions.   I was assured that Dell would provide keys for both too. 

 

The machine I received is running 32bit and there doesn't seem to be a way to change it.  No one can tell me how to get a 64bit key so I can get to the extra memory.  What is the point of advertising a maximum memory of 8GB if you don't provide a way to use it?