Northwood-B is the quad pumped 133MHz FSB version of the existing Northwood-A Pentium 4 processors on the market.
The current Northwood-A processors utilize a quad pumped 100MHz FSB (400MHz effective), whereas Northwood-B will utilize a quad pumped 133MHz FSB (533MHz effective).
The ETA for Northwood-B is sometime in May. It's very likely that you'll have a Northwood-B in your hands by June, if you're talking worse case scenario. May is my guess though...