I've said it before and I'll say it again: Windows Media Center is a better DVR than TiVo. It has a vastly superior program guide, a much prettier Netflix interface, and a total lack of monthly fees.
The key ingredient to a successful WMC setup is a CableCard tuner. These were few and far between until a couple months ago, but now you have several good options.
Like this one: Newegg has the SiliconDust HDHomeRun Prime HDHR3-CC CableCard tuner for $169.99, plus $6.98 for shipping. The list price is $249, and most online outfits sell it for around $229.
The HDHR3-CC offers three digital tuners that can pull down HD and premium channels alike. (Sorry, no on-demand or pay-per-view, though.) All you need is a CableCard from your cable company. The one I'm renting from Comcast costs me all of $1.50 per month; I think I was paying $13 to $14 for a DVR box.
What's unique about this particular tuner is that it plugs into your home network router, meaning you can share its tuners with multiple Windows 7-powered PCs: one in the den, one in the bedroom, and so on. (Ideally, however, you'll want a wired Ethernet connection between those PCs and your router.)
There's even a companion iPad app, though it's pricey at $17.99 and not very good.
My only real complaint is that you can't plug the HDHR3-CC into a single PC if you prefer that kind of configuration. But for multi-PC households, the HDHR3-CC is a steal at $169.99. Grab one while it's on sale!