Just dish out the extra cash and get the 1.6a, the 1.7 celery's a williamette core, not northwood. You won't see northwood celery's until around the time of prescott.

I suggest the Asus P4B266-c if you're going to go i845, since it has the jumper/jumperless 3:4 memory divider trick.

I'd go with the P4S533 over that any day though, but that's your decision.