Ah! Turns out that this TiVo was purchased from weaKnees with an upgraded 320GB hard drive. And the warranty page that came with it is for three years, although I don't recall purchasing an extended warranty. (I've got two separate warranty pages that say this, and I purchased two TiVos from weaKnees, so this page definitely came with the problem TiVo.) So now I'm emailing weaKnees to see how to handle a possible warranty repair.