Can you use a digital camera as a webcam, if so how? (In particular the Kodak C643 model)?

It doesn't appear as though you can use this particular camera as a webcam, but it does shoot videos that you can upload.

yes you can. the camera would have come with a cd full of software that has a step by step guide. If you lost the cd you can download the program from
www.downloads.com

if it has a usb out let then plug her in matey(your computer will say found new hardware) if you have a cd thats even better , its like pretty easy after that

Yes you can!
see if your digital camera has a line out video?
if yes you must have a capture card,any tv cad which accepts line in video.
after all you can use your digital non-webcamera as webcam
i do it with my 2 canon A70 and Canon S3-IS
it works great