I think you're essentially stuck with opening it up and finding the PLL chip and reading the part number on it, then hoping SetFSB (or whatever you prefer) supports it.
Atom cpus downclock a lot when they aren't loaded anyway, down to 800 actually i think. If you set it for Maximum Battery in power profiles (don't know what it's called in vista, that's it's XP name) you'll see the CPU lock itself to 800mhz or so (i might be dreaming and it's 1200, today isn't a good brain day, i woke up about half dead, been improving so i'm only about 10% dead now, but my brain is largely in that 10%).
