Get Winroute Lite, which is free.

You can put 2 NICs in the machine with the 10. connection - the other with a 192.whatever.1 connection - set up a second IP address 192.whatever.2 on that card, NAT host-to-host from that second IP to 10., then have people telnet to 192.whatever.2 and it should route through to the 10. interface.

This also sounds sort of like a "proxy ARP" situation but that's probably a slegehammer for a peanut.