Or you could use Dial Up :-)

Works for me - and my S1 Tivo. Not sure how the current gen Tivo can be configured to do that, using the host PC as the gateway.

Static IP on Win7 which is acting as the gateway, static IP on the Tivo. I did try with ICS, but that just messed up everything. There were some hiccups with the DNS lookups, but AFAIR the S1 Tivo looks for IP rather than DNS names for retrieving the EPG.