Apple has made a new portable wireless basestation, and it can stream
music throughout your home sound system. Well, it says, or i predict
that it only works with the airport extreme basestation, because of
the audio port on the basestation. Is it also compatible with a
linksys wireless-b router? And if not, is there any way it can be
connected with the router and stream music using airtunes technology?
If not, what routers could be compatible with the portable wireless
basestation and stream music with itunes? (it's called airtune
technology or something)

Airtunes depends on iTunes. Seems like iTunes will check the network
for the adapter (that should have a name) and then it will be
identified and sent signal(music) if properly configured it should
work. Since this is through wireless it should work with any type of
wireless antena (router).

http://www.apple.com/airportexpress/

It claims that "If you already have a wireless network in place, you
can use AirPort Express to add music to its capabilities. Let?s say,
for example, you have AirPort Extreme set up in your den. There?s no
need to scrap this setup and create a whole new one with an AirPort
Express Base Station, your DSL or cable modem, printer and stereo all
in one place. Simply connect AirPort Express to your stereo in your
favorite music room and plug it into an electrical outlet ? it
wirelessly links to your existing network, letting you play your music
in your room of choice without moving anything or connecting anything
else."

So I believe it would work with any Wireless B or G network.

Found something else.  It will stream music just fine with any
Wireless router, however, "AirPort Express can extend the range only
of an AirPort Extreme or AirPort Express wireless network."

It will only act as a Bridge with Apple's Wireless Access points.  Hope that helps