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.
Please try to use the microscope with Photo Booth first before downloading the driver, and let me know in the comments if that works.