I did not detect any "smarts" in the dock that could be communicating with the Streak.
 
That said, there are many ground pins on that HDMI connector.  It is very likely that the dock or other peripherals are identified by combination of those ground pins.
 
When I put the Streak in the dock, It gives me an option to mute the sound, with 2.2, it now also goes into docked mode (the clock app).  When I connect my mini USB adapter (with or without being connected to USB power), it does not do this.  This means it knows when it is in the dock.
 
With due diligence,  it should be safe to try different ground combinations.  I would not just do it randomly, and I would not connect to anything but ground.  For example try grounding ground pins in groups,  for example what happens if you connect the 2 high current grounds? (7, 16)  That would probably only happen in a dock (I don't think HDMI High-current Power cables were ever planned or made.)
 
I would also like to make an Audio cable so that I can connect USB power and the audio with one connection in the car.  If I ever get around to this, I'll post what I find.
 

Hello,
 
I'm interested in making a one-off PDMI to HDMI cable for the Dell Streak (If we are picking nits, it's going to be a PDMI to DisplayPort to HDMI cable--see below). I refuse to pay $50 for some copper, a piece of shiny molded plastic and a few resistors and caps. However I do want to display my Streak 5's output on my TV, if only to view photos and videos with the inbuilt video player. (I'm crossing my fingers for NetFlix, but I'm not holding my breath.)  
 
I'm assuming the following:
- PDMI has a bunch of stuff (USB 2.0, USB 3.0, analog, audio, DisplayPort)
- DisplayPort is a subset of PDMI (well, kind of; PDMI only uses two of its four 'lanes' and the auxiliary lane)
- DisplayPort isn't officially HDMI-compatible but can detect VGA, DVI or HDMI and output the appropriate signal - maybe through the 'Hot Plug Detect' pin?
- The Dell Dock has no active circuitry; the DisplayPort-to-HDMI conversion is done on the Streak itself
- The Dell Dock with HDMI out has some pins grounded (which pins?) that trigger the "Wanna display HDMI?" software controls on the Dell Streak's firmware
 
Anyway, my plan is to buy a $5 PDMI-to-USB cable and a DisplayPort-to-HDMI cable. Based on the specs and pinouts for PDMI, DisplayPort and HDMI, I will attempt to hook the thing up to my HDMI TV. I am also going to break out and ground random grounds on the PDMI cable together (as John suggests above) to see if I can get the Streak to respond appropriately.
 
I'll report back here soon. Wish me luck! (And if anyone who owns a dock wants to put an ohmmeter to any of the ground pins on the thing--that'd be 2, 7, 13, 16, 18, 25, 27 and 29--I'd love to hear which ones are fused together )
 
PDMI spec: http://en.wikipedia.org/wiki/PDMI
DisplayPort spec: http://en.wikipedia.org/wiki/DisplayPort
HDMI spec: http://en.wikipedia.org/wiki/HDMI
DP-to-HDMI adapter ($3-5 w/shipping): http://shop.ebay.com/i.html?_nkw=displayport%20hdmi
Streak USB cable ($3.50 w/shipping): http://shop.ebay.com/i.html?_nkw=streak+usb+cable

USB spec here, also, for posterity: http://pinouts.ru/Slots/USB_pinout.shtml

Well today I tried putting 3.3V on the Hot Plug detect pin and it didn't do anything. Also tried measuring pin 23 which should have voltage but it didn't. I would really like to make my own cable so that I could use it in my car.
 
Can someone take some really detailed photos of the dock PCB board? Detailed enough that I can see where the traces are running.
 
Thanks in advance!

Hi Guys
Have you made further progress??
Is there confirmation for:
Pin 7 = Grnd
Pin 8 = Right audio line out
Pin 9 = Left audio line out
Pin 10 = Audio ground
Shorting Pins 7 & 9 starts docking mode, so the built in speaker can be shut off ??
Alternatively, any ideas as to which colours are which in the OEM cable?
I will happily sacrifice a cable if I know which is which!
Many Thanks
Good luck with this, as if it can be done, I and my ears will be SO happy !