In the "Select a geographic type" menu, choose "block".
Select a state, then county, and a block group before you are offered a menu of blocks. Select one or more blocks by clicking the "add" button.
Click "show results" to get up the table menu. Select table P15 (Households), and click the "add" button.
Click "show results" from this screen to get the number of households.
Incidentally, I doubt that you would know the number of the block you are interested in, so at step 2, you might want to try the "address search" tab near the top of the screen, where you can enter the address, click "go" and the census block you are looking for will be displayed for you for selection. Sjakkalle(Check!) 06:22, 16 September 2008 (UTC)