Downloading the HP Universal driver, followed by the HP Color Laserjet 3500 driver for Vista worked for me. Thanks very much for the solution. Note that I have 64-bit. Also note that after installing the 3500 driver for Vista, I had to update the driver (i.e., go to Start, Computer, System Properties, Device Manager, Other Devices -- then right click 'Update Driver' and follow the prompts). And voila!
Very disappointed in HP for its failure to support LaserJet 3500/Windows 7 customers.