Query in SQL Server 2008

I would like to develop a query in SQL Server 2008 that will fetch me the solution for “Month—Collection Sum” from a three columned table.
The columns are ID, Amount Collected and Date. For eg.,
Jan 2011 Collection sum should be the sum of all the entries in column Amount Collected dated on or before Jan 2011.
How can I make this happen? Please help.
