Dissolve the rennet tablets in 1/2 cup warm (NOT HOT) water; stir until dissolved.
In a large glass or stainless steel bowl, combine the skim milk, buttermilk and rennet mixture; Stir.
Cover bowl with plastic wrap.
Let stand at room temperature for 24 to 36 hours or until the mixture separates into curds and whey.
The large white curds will sink to the bottom of the container while the watery, whey rises to the top.
Line a colander with 2 slightly dampened layers of cheesecloth, letting 2 inches hang over the edge of the colander.
Place the colander over a large bowl. Slowly pour in the curds and whey. The whey will drain off; discard it or, if you are feeling ambitious, you can use it to make ricotta or as a substitute for water or milk when you are baking.
Leave the curds, covered and refrigerated, to continue draining and solidifying for another 24 hours or so before using.
Fresh homemade cream cheese lasts about 1 week in the refrigerator.
~NOTE~ Central Market and Whole Foods both carry tablets of rennet, an enzyme that makes milk coagulate.