Retail versions of Ultimate (full and upgrade) come with two DVDs, one for
32 bit and one for 64 bit, commonly called the x86 and x64 versions. The
product key will work for either version, though only one can be installed
at a time.
Other retail versions of Vista only come with the 32bit DVD and a coupon to
send for the x64 DVD for a small fee. OEM versions come with only one DVD
for the version purchased. There is no comparable offer to get the other
DVD.
