Okay here is the correct answer i think your looking for
There is a glitch/bug in smp atm about not being able to make snow blocks out of snowballs, Also I wouldn't be making your house out of those snow blocks anyway when this gets fixed in possibly the next update on April 5th 2012 (1 day away) Because in 1.2.5 (5th April) or 1.3 (Late April) Snow blocks will melt with +7 velocity from the suns rays or other lighting blocks such as Torches, glowstone or redstone torches, the suns rays are +15 as the same for glowstone and torches, and redstone torches have a velocity of +7 (I believe) To make sure snow does not melt you will need to have your snow block 15 blocks away from a torch with no sun or any light for that matter.
I hope this helped you out