actually, I think I've figured it out.
This affects all the new macs with the 1.3MP iSight. I'm pretty sure they're on the SR MacBook Pros and the current Al iMacs. The supplied driver that comes with bootcamp 1.4b is probably for the older 0.3MP iSights.
Anway, here's what I had to do for a "temporary" solution so that it works on yahoo messenger.
You'll have to extract the apple isight drivers from the bootcamp drivers CD. I used winrar to extract them all to a folder. You'll wind up with 8 files. The file that you'll have to modify is the isight.inf file.
Open the isight.inf file in notepad or some other text editor.
Find the following entry. Change the value to coincide with your correct device ID. which is "8502"
[Apple]
%iSight.DeviceDesc%=iSight,USB\VID_05AC&PID_8503&MI_00
Next, go into the device manger and update the driver for the USB_Video device under the section "imaging devices" Click on advanced and then choose "have disk" and point to your newly update windows isight.inf with the modified code. Next reboot... but it won't work. correct. this is a non-working driver for the new 1.3MP isight. To get it to work again, just update the driver using windows "device manager" and this time instead of using choosing your own driver, let windows "choose driver automatically."
reboot and you'll find that yahoo messenger works correctly now.