Its rumored that Apple's Localtalk Bridge can route TCP/IP over Localtalk if installed on a machine with Open Transport 1.1.2 or later installed: http://lowendmac.com/tech/ip_on_localtalk.shtml

Information on installing Localtalk Bridge with download link: http://support.apple.com/kb/DL1258

If Localtalk Bridge doesn't work, IPNetRouter will do the job, but is commercial software: http://www.sustworks.com/site/prod_ipr_overview.html

Apple also sold a product called "Apple IP Gateway" but it is no longer available.