Two Tuners
If your two tuner question was directed towards PIP capability, you may be able to find an UltimateTV unit which had two tuners and performed PIP in the STB and sent it through a single output to the TV. They stopped making the units, but you may be able to find one on eBay. Check out the UltimateTV board on AVSForum to learn more about them and some of the issues users have had.
Late summer 2002, after MicroSoft announced they had stopped making the units, Best Buy was clearing them out. I bought one for $25 and one for $40. I'm down to one tuner on one of the units, but otherwise have had very few problems.