Ever since TiVo and ReplayTV hit the scene back in 1999, digital video recorders (also known as DVRs or PVRs) have promised to change the way we watch TV. They've been described as "smart VCRs" or "VCRs on steriods," they're easy to use, and they perform some nifty tricks such as pause live TV and allow you to record every episode of your favorite shows automatically. That's all true, but with more DVR options hitting the market--from the generic DVRs that your cable company may be offering to bona fide TiVo units to DVD recorders and hard-disk recorders--picking the right one is becoming a serious challenge. With that in mind, we've come up with this short guide framed by four simple questions to help you sort through the dizzying array of choices.