Karen,
Just a word of warning about flavoring the milk. Only do it if you are prepared for the possibility that he will only accept milk if it is flavored from here on out. I used Ovaltine and a small amount of chocolate syrup when I was transitioning DD1 to the sippy. Now, she is 3.5 years old and refuses to drink any milk but chocolate, and if we are at home, it must be warm (but she is perfectly fine drinking it cold when we are out somewhere). I use only about 1 TBSP of Ovaltine for 6-7 oz milk, and honestly, it does not add all that much calories or sugar. It is more the principal of the fact that she will only drink it flavored that is a problem.
This is something that really irritates DH, and for DD2, who is now 7 months old, I am going to try and force the plain milk thing before giving in and flavoring it so quickly (with DD1 I started flavoring after only a few times of her rejecting it).
As someone on this board told me once "start as you mean to continue".