Simple problem but with a slightly indirect solution. The LAN consisted of mixture of 32 and 64 bit versions of Vista with the printer, an Epson CX6400 on the 32 bit Vista machine.
It was identified that there were Vista drivers (32 and 64 bit) for the CX6400 but these were only available via Windows Update. The difficulty was getting the printer shared with the correct driver on the the 64 bit machine. The printer drivers are
not available to download as seperate .inf installation.
With the printer switched on the 32 bit machine found it and gave the option to locate and install the driver via Windows Update. This worked fine. On the LAN the 64 bit machine could see the printer and recognised it needed a driver and offered to download it from the 32 bit machine - but of course it was not there! Windows update had only installed the 32 driver and not the ones for other OS's. The option to make these avaaible was ticked in the printer setup to allow other OS drivers to be stored but this can be only set after the single driver has been installed via windows update.
As Vista 64 but could not find the driver on the 32 bit Vista machine it offered the "Have Disk" option of supplying an .inf file, which of course was not available. It did not go to the internet and try with windows update to get the correct Vista driver.
The only solution was to physically attach the CX6400 to the Vista 64 bit machine, let windows update install the 64 but driver and then return the printer to the 32 bit machine. This time when adding a shared printer it had the correct driver installed and all was OK. The "local" CX6400 that was no longer present and could then be deleted after the other printer was shared.
You would have expected windows update to check the Internet what was available not just offer a disk.