It seems like for some reason this network printer is not exposing a 32-bit driver,
which is more than puzzling, even worrisome.
It might possibly mean a defective printer firmware.
I can detail below the procedures that usually solve such problems.
If none of them works, then something is wrong with the printer itself.
The printer on the Windows 7 x64 must be shared, let's say it's named "PrinterName".
You may find your printer software on this Support page.
Download the driver for Windows 7 32-bit and install it locally.
You should then be able to see the printer in network neighborhood and use it.
If that doesn't work, then you could first connect the printer to the Windows 7 32-bit
computer and install it as a local printer, then move it back to its computer and
convert the local printer to network printer as detailed in
this answer.
Still another method is to use the Add New Printer wizard,
start a Local Printer, select New Port of type Local Port,
and type \\MACHINENAME\PrinterName.
If you need to select a driver, select yours from the list.