ORDER BY question

I have two tables, table A contains users (id, username, password) , and
table B contains a row that signifies the 'owner' of each particular entry,
referencing an id in A.

so example

table A
id  username password
------------------------
1   me           *****
2   you          *******

table B
description           owner
-------------------------
'something cool'   2
'another thing'      1


What I want to do is do a query where I order table B by owner, but
alphabetically by username. The problem, obviously, is that table B only
contains id's (numbers, indexing to A), which don't correspond to the
alphabetical order of the usernames.

I'm not very familiar with subqueries, but I expect I should be able to
somehow select ID's from table A ordered by username, and use this index to
order table B by owner.

Hopefully I made sense.

Thanks in advance!