How about Nicecast?
That wouldn't be in sync, so it wouldn't help Andrew.
The Airport Express (802.11g) price has dropped from $129 to $99 in the Apple Online and Retail Stores.
And it's often been available for that price as a refurb...
Still, this would be as reasonable a solution as any other suggested
well, no other "solution" has been suggested.
And I understand Andrew's point--if you've just spent $600 or $700 to put a mini in another room, hooked up to the TV and stereo there--it isn't unreasonable to think that there would be an Apple-delivered solution in software which could emulate the Airtunes in-sync streaming (local and multiple locations all in sync) that you get with an Airport Express.
If I just spent $700 to network a bedroom with a mini, I wouldn't be eager to drop another $99 for an Express, either.