How do I total up the amount of an item by month and also name?

For example:
Colum A: Colum B: Colum C:
Dates: Units Sold Seller:
1/5/05 8 Josh
1/6/05 10 Josh
1/15/05 7 Rick
2/8/05 1 Josh
2/20/05 13 Rick
3/5/05 25 Rick

So I am trying to set up a chart where January Gives the totals for Josh and
Rick in seperate cells and etc. for each month.