I was off the 'Net over the weekend due to a broken broadband drop cable between the street and our house,
so I wasn't able to try the new Parallels 8 kit to which someone kindly posted a link.
Alexdaft - I think your problem might be related to this general USB device non-start issue, although you may need
to check the settings presented in the Mac OS X toolbar for Parallels (when you have Parallels up and running
and 'focused') because it's possible that Parallels doesn't know that it's supposed to present the WebCAM to
your guest OS (Windows, or whatever). I spent a fair amount of time clicking and unclicking my Serial/USB
(FTDI chip-based) adapter and my USB Sound Card over the weekend. Parallels and/or Windows (and Mac OS X?)
might think that the WebCam is a USB device (and might well be, even if it's just in silicon, with no cables )

.
However, I was able to do a modicum of testing offline using the previously downloaded Parallels 7 kit to which
I posted a link earlier, and discovered that although my FTDI/serial line and USB Sound Card "worked" (in that
my applications were able to function properly in their individual roles), I did notice that I did not have any
"Windows sounds".
Normally, Windows 7 would see two audio devices - the built-in one in the iMac as presented to it by Parallels 7,
plus the USB Sound Card. I had Windows 7 configured to route the normal Windows 7 emissions ("Ding", etc.)
back through Parallels to the iMac hardware, and the USB Sound Card was reserved for use solely by my
applications, thereby ensuring that Windows 7 sounds did *NOT* go through the USB. (This is a critical
requirement - I'm using the USB Sound Card, a Signalink USB, as an interface to my amateur ["ham"] radio
equipment and the applications perform DSP magic to create "tones" that transmit digital data through the
audio/microphone circuits of my transceiver - transmitting a Microsoft "ding" in the middle of that is a "no-no"!).
However, now Windows 7 refuses to "see" the Parallels-routed iMac hardware and thinks there is only one
sound card on the system - the USB one. Obviously, I had to then turn off all Windows Sounds from within
one of the various Windows 7 system management GUIs.
This is beginning to feel like a sausage-squeezing exercise, whereby what's squirting out the ends can be pushed
back in at the expense of other stuff squirting out the sides. I'm going to try the Parallels 8 kit now (after I
finish my backups, thank you...) and see if there's been any improvement over the weekend, but given the
track record of Parallels "support", I'm not optimistic.