Vista - BeginExecuteNonQuery IAsyncResult

So im trying to do a SQL BeginExecuteNonQuery which seems to kick off fine
the problem is detecting when its done.

i do something like this to start it

$result = $sqlcmd.BeginExecuteNonQuery()

that kicks off no problem (im having it run a backup, i can watch it create
the backup file)

if i do $result.iscompleted i get nothing. if i do just $result i get two
empty lines.

if i do $result | get-members i get this


TypeName: System.Data.Common.DbAsyncResult

Name MemberType Definition
---- ---------- ----------
Equals Method System.Boolean Equals(Object obj)
GetHashCode Method System.Int32 GetHashCode()
GetType Method System.Type GetType()
ToString Method System.String ToString()


so its a DbAsyncResult, which i guess if fine but MSDN refers to an
IAsyncResult. i tried to create the IAsyncResult with a new-object prior to
running the command but it doesnt find a constructor it likes...

when i EndExecuteNonQuery i get a -1 (i assume thats a success?) and it
seems ok

anyone know what im missing?

Thanks
Justin