Migrate Time Machine backup (10.6.x) to MacBook Pro (10.8.x)

On a USB drive, I have a Time Machine backup--from a Macbook running (10.6.x).

I'd like migrate this account from its TM backup to a Macbook Pro (10.8.x)

I've plugged in the USB drive to the new machine, it mounts and works perfectly.

But using Migration Assistant, I select "From a Time Machine backup or Another disk".

The disk is never found, the "Looking for other Comuters" spinner never stops.

How the heck do I get this account to the newer machine?

Thanks!