I just brought Maplin's USB Digital Microsoft with 400x magnification, which is advertised as having Windows-only drivers. System Profiler identified the chipset as being from Vimicro Corporation. I went to the Driver Download section of their website and downloaded (and installed) the DRV_ZC0301PLus_070305 driver. I then opened up Photo Booth, and was able to select the Vimicro camera as the video source. What I should have done was just try and access the Microscope using Photo Booth before I installed the driver, as I half suspect that there was no actual need to install that driver.
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Please try to use the microscope with Photo Booth first before downloading the driver, and let me know in the comments if that works.