Concat groups in SQL Server

If I have a table like this:

+------------+
| Id | Value |
+------------+
| 1  | 'A'   |
|------------|
| 1  | 'B'   |
|------------|
| 2  | 'C'   |
+------------+

How can I get a resultset like this:

+------------+
| Id | Value |
+------------+
| 1  | 'AB'  |
|------------|
| 2  | 'C'   |
+------------+

I know this is really easy to do in MySQL using GROUP_CONCAT, but I need to be able to do it in MSSQL 2005

Thanks

(Duplicate of How to use GROUP BY to concatenate strings in SQL Server?)