Printing to the non-AppleTalk-enhanced ImageWriter and ImageWriter LQ is indeed possible with this driver from OpenPrinting:
http://www.linuxfoundation.org/en/OpenPrinting/MacOSX/imagewriter
They recommend the well-tested Keyspan USB to Serial adapter, and suggest others may work as well.
The package installs a number of different drivers -- just delete the ones you are not going to use.
One caveat is that the intricate "last-form-tearoff" paper positioning we took for granted in OS 9 is not supported. Printing tends to stop about an inch below the tear-off position. Do not roll the platen up to tear off, unless you immediately roll the platen back down to the red line before printing resumes. (Rolling the platen by hand changes the paper position relative to top-of-form.)
If you have another AppleTalk printer, such as a LaserWriter, it may be preferable to acquire an AppleTalk option card for your ImageWriter II or LQ and use the AppleTalk version of the driver over Ethernet with an AppleTalk-over-Ethernet to AppleTalk/LocalTalk Bridge device.