T-SQL (SS2K8) :: How To Group Total Count Of Similar Items

We sell & ship packages that contain multiple items within them. The actual package (we call it the "parent item") is in the same table as the items within it ("child items"). If the record is a child item within a package, its "ParentId" field will contain the ItemId of the package.

So some sample records of a complete package would look like this:

ItemId | ParentId | Name | QtyAvailable
----------------------------------------
1 | NULL | Package A | 10
2 | 1 | Item 1 | 2
3 | 1 | Item 2 | 3

ItemId's 2 & 3 are items contained within the ItemId 1 package.

Now however, the client wants us to build a report showing all packages (all items where ParentId is NULL) however, they want to see the QtyAvailable of not only the package but the items as well (a total of 15 when using the example above), all grouped into a single line. So a sample report line would look like this:

Name | Available Qty
--------------------------
Package A | 15
Package B | 100

How can I do a SELECT statement that SUMS the "QtyAvailable" of both the parent & child items and displays them along with the package name?