Celerons have always really slacked in gaming, the 2.2ghz Northwood will be better, you'll really notice it at gaming, and it would be around equal with the Celeron in about everything else...
I know from experience, that Celeron's arent good for gaming. I had a Celeron D 2.6Ghz and a 9600XT, and I couldnt play Halo at all, but with my other P4 I played it maxed out at a constent framerate.
If you guys couldn't tell, WoW isn't a very demanding game : / the older type of celeron D @ 2.8ghz can play it fine, thats what I had in this PC a long long time ago.