CableCARD from your cable co' and if you're hoping to save a few bucks by using a multi-stream (aka M-Card) CableCARD in your TiVo HD -- does any other 3rd party host device even support M-Cards? -- then you have an even harder road ahead than most. Recently good 'ol S&V Mag braved the trail and came away semi-scathed. Lucky for us, they documented the journey and have written up a pretty comprehensive list of pitfalls to watch out for. Some are pretty obvious, like the need to be persistent when you meet the cable co's resistance to all things CableCARD, but it's a must read nonetheless. Oh, and one more thing, make sure the card actually says Multi-Stream on it before you even bother inserting it, as many cable co' employees think M-Card means Motorola card!