I have a Windows MCE 2005 PC at home and I hooked up CallerID on my MCE 2005 PC. It's pretty cool, as can be seen by this screenshot of someone using this app on their MCE PC hooked up to a TV. (Click on the screenshot to go to the webpage where you can download the CallerID application for MCE.)
I also have integrated text-to-speech using Microsoft SAM, so it actually recites the name of the person calling using my home theater speakers. The CallerID application I use is a bit different than the web link I list above (there are a few CallerID applications for MCE). I forget the name of it now. I'll have to check when I get home. In addition to TTS it also features a phone log, so I can see who called me.
In any event, there apparently is now a plugin for Tivo so you can display your CallerID in your TV using your Tivo box. I still prefer MCE over Tivo, but Tivo certainly has a dedicated community!
TiVoBlog posts about how to get caller ID on your TiVo. This has been something that has been available for quite a while now on the Media Center PC. It's a nice feature that I don't personally use because my HP873N doesn't have an expansion slot for a modem in it (I'm using it right now for a Gigabit Ethernet card). More...(Thomas Hawk) Read more from this post.