As Darren said, the upgrade from 1.4 to 1.6.2 has been fairly painless for most people.

The fault in 1.4 was with the reporting of the IP address on boot. The reporting doesn't work correctly, but this didn't stop the tivo from obtaining an address. The updated file is available HERE copy it into /hack/bin.

Even without this file, if you check your router a couple of minutes after the TiVo has completed booting up you should see what IP it has given it.

Also you could use an IP scanning program like IPscan to find where it is on your network.

Peter