For auxiliary inputs Blaupunkt has a reasonable setup.  On most of the DIN
chassis (Reno, Sydney, Miami, Orlando, Los Angeles for certain) there is an
auxiliary input at ~1200mv RMS available on the rear panel.  It requires a
cable and plug to provide either 2 RCA or one 2.5mm stereo jacks then just
plug in the PC and it's showtime.  Sound volume is controlled via a remote
to the "head unit" or radio chassis.  Works for me as the basic spatial
effects are available via the Balance and Fade controls on the head unit.
These units can also accept various steering wheel mounted remotes.  RC-10
RC-08 etc.

In addition most of these head units will accommodate the MD01 Microdrive
1GB MP3 system, a smallish box that interfaces a 1GB or larger Microdrive to
the head unit using the BP CDC protocol to play the music.

Neat stuff, sounds good, matches the decor.

For the CD72 and MP72 there are actually two external inputs one which can
be dedicated to a CDC protocol device (CD Changer) and the other some other
source such as Sirius radio, shameless plug but hey I LIKE it.

Of course the units also have other kewl features (amp inputs/control,
muting for phone/NAV, automatic antenna).

Visit www.bluespot.co.uk for tech details on most of the Funline, T-Line,
and Skyline Blaupunkt offerings.

I have found that an FM modulator works pretty well except in locations
where all the channels are taken with high wattage Rap, Religious, or
WrongWing talk shows.