lurkswithin gave a pretty good summary.
I have to agree about the memory configuration.
Not being matching pairs is a little strange coming from a big retailer.
That said it's quite a lot of memory for the other specs. Which is the most desirable spec for photo editing.

Also if you intend on using other software or hardware that you already own (photo editing, printer/scanner etc) you'll want to check if they have Vista 64bit drivers (hardware), compatibility (software) so you will know if they will work with the new system.