The Apple iPhone doesn't work with 64-bit versions of Windows . Although the number of 64-bit installations of Windows XP and Vista can probably be counted on the back of a stamp, the problem has reared its ugly head for a number of early adopters.
And they must truly be early adopters, for to have the 64-bit version of Vista installed is to be brave. The error message that appears is simple: "The software required for iPhone is not installed."
Slightly more interesting is that the author of a post on Slashdot says he wrote on the support forum about the problem, but the thread was soon removed.
However, Apple can't really be blamed - the small print of the iPhone says that 64-bit versions of Windows aren't supported. But it's buried deep within a support article, rather than being listed on the basic system requirements page. Oops.