It theoretically should be, but the default Vcore of a Willamette is ~1.75V as opposed to the ~1.5V of the Northwood, so if you can find info on >1.8V, it should work. All of the links I had on this seem to be no longer functioning.
But as Thugsrook said (and if anyone should know about overclocking, it's him), Willy's really don't OC well. In my limited experience (2x 1.7GHz Willy Celerons), they only got to about 1.9GHz no matter how much voltage I pumped into them... Not to mention that my PIII Celeron at 1750MHz is WAY faster than the Willies!