I don't believe there is a 64-bit version. I am running Endian on a Core2Duo 2Ghz with 4GB of memory and on the WI, I see 3024MB of memory. You might need to perhaps change a setting in your BIOS.
I'll have a look at the RAM settings in the BIOS again during the week... BIOS definately detects 6GB of RAM though.