I've had my Sony Digital 8 Camcorder for while , but only today desided too try the webcam feature. Like you had no idea how too do it and had misplaced the original CD that was supplied from new. While searching I fell upon your post here and as I have it working now, I thought I'd answer your question.

First off I'm assuming you have a DCR-TRV**** series camcorder and the USB cable supplied from new, also I'm assuming you haven't got the original CD or USB drivers.

It's actually not that hard at all too setup.
Goto the Sony website (either www.sony.com or like i did www.sony.co.uk).
Then goto support and enter the model number for your camcorder (e.g. DCR-TRV****) located on the bottom of the camcorder.
Download and install the USB driver.

Now turn the camcorder on , go into the menu (mine has a touch screen this is where things may differ alittle but i'd assume the menu's will be very similar if yours uses buttons instead.)
When I select P-Menu on the screen, I get the 1st menu open , top left button marked MENU, this takes me too the main configuration of the camera.
In those sub menu's your looking for the option called USB-CAMERA
For me its P-Menu / Menu / Standard Set
Scroll around that sub-menu too Usb - Camera.
You need too turn that on, as by default its turned off.

Now just connect the USB cable too the camera and the computer.

The camera's USB connector is located underneath the cover located on the front righthand corner under the light (when veiwing the camera from behind - as if you were using the view finder). The connection is marked DV.

The PC should pick up the camera and promt for the driver , click look for driver automatically , as you already installed the driver pack and the PC will do the rest.

Yahoo! messenger will pick the camera up the next time you run it, just click Messenger / My Webcam , too test it from the file bar in messenger.

Thats all I had too do too get mine working and I would think it will be just as easy for you too do the same.

I tried too be a thorough as possible too hopefully make it easy too understand.

Hope it helps